diff --git a/calendar/api_event.go b/calendar/api_event.go
index dbb551b..4464d69 100644
--- a/calendar/api_event.go
+++ b/calendar/api_event.go
@@ -27,17 +27,22 @@ func ApiEventQuery(c *gin.Context) {
 		}
 		var result *gorm.DB
 
-		if grp != "" && auth.ACHas(c, auth.ADMIN, auth.SYSTEM, grp) {
-			var grp_id uint
-			db.Raw("select id from groups where name = ?", grp).Scan(&grp_id)
-			if grp_id == 0 {
-				panic(errors.ErrorNotFound)
+		if grp != "" {
+			if !auth.ACHas(c, auth.ADMIN, auth.SYSTEM, grp) {
+				panic(errors.ErrorForbidden)
 			}
-			result = db.Find(&events, "`group_id` = ? ", grp_id)
+			result = db.Find(&events, `event_group_id in (
+				select id from event_groups where group_id = (
+					select id from groups where name = ?
+				)
+			)`, grp)
 		} else if !auth.ACHas(c, auth.ADMIN, auth.SYSTEM) {
-			result = db.
-				Find(&events, "`group_id` in (?) or group_id = 0",
-					db.Table("groups").Select("id").Where("name in ?", cl.Groups))
+			result = db.Find(&events, `event_group_id in (
+				select eg.id from event_groups eg where eg.group_id in (
+					select g.id from groups g where g.name in ?
+				)
+			)`, cl.Groups)
+
 		} else {
 			result = db.Find(&events)
 		}
@@ -60,15 +65,28 @@ func ApiEventNew(c *gin.Context) {
 	if e.Start.IsZero() || e.End.IsZero() || e.Start.Before(e.End) {
 		panic(ErrorInvalidTime)
 	}
-	if !auth.ACHas(c, auth.ADMIN, auth.SYSTEM, e.GroupName) {
+	cal := 0
+	if db.Raw("select count(id) from calendars where id = ?", e.CalendarID).
+		Scan(&cal); cal != 1 {
+		panic(errors.ErrorNotFound)
+	}
+	if !auth.ACHas(c, auth.ADMIN, auth.SYSTEM, e.EventGroup.GroupName) {
 		panic(errors.ErrorForbidden)
 	}
-	if err := db.Create(e).Error; err != nil {
+	if e.EventGroup.Name == "" {
+		e.EventGroup.Name = e.Name
+	}
+	if err := db.Transaction(func(tx *gorm.DB) error {
+		if err := tx.Create(e).Error; err != nil {
+			return err
+		}
+		return nil
+	}); err != nil {
 		panic(err)
 	}
 	history.Send(history.Info().
 		Nm("Create").
-		Grp(e.GroupName).Bd(e).
+		Grp(e.EventGroup.GroupName).Bd(e).
 		Iss(c.GetString(auth.GinUserKey)).
 		Msg("Event created"))
 	server.OK(c, e)
@@ -90,7 +108,7 @@ func ApiEventUpdate(c *gin.Context) {
 	}
 	history.Send(history.Info().
 		Nm("Update").
-		Grp(e.GroupName).Bd(e).
+		Grp(e.EventGroup.GroupName).Bd(e).
 		Iss(c.GetString(auth.GinUserKey)).
 		Msg("Event Updated"))
 	server.OK(c, e)
@@ -107,13 +125,16 @@ func ApiEventDelete(c *gin.Context) {
 		panic(err)
 	}
 
-	err = db.Delete(&Calendar{}, "id = ?", id).Error
+	err = db.Delete(e, "id = ?", id).Error
 	if err != nil {
 		panic(errors.NewError(404, err))
 	}
+	db.Exec(`delete from event_groups where id = ? 
+	and 0 = (select count(id) from events where event_group_id = ?)`,
+		e.EventGroupID, e.EventGroupID)
 	history.Send(history.Info().
 		Nm("Delete").
-		Grp(e.GroupName).Bd(e).
+		Grp(e.EventGroup.GroupName).Bd(e).
 		Iss(c.GetString(auth.GinUserKey)).
 		Msg("Event Deleted"))
 	server.OK(c, "ok")
diff --git a/calendar/calendar.go b/calendar/calendar.go
index 40bb22b..0dbc0d8 100644
--- a/calendar/calendar.go
+++ b/calendar/calendar.go
@@ -14,6 +14,11 @@ var l zerolog.Logger
 
 var db *gorm.DB
 
+var color []string = []string{
+	"red", "pink", "purple", "deep-purple", "indigo", "blue", "light-blue", "cyan", "teal", "green",
+	"light-green", "lime", "yellow", "amber", "orange", "deep-orange", "blue-grey",
+}
+
 type Calendar struct {
 	ID string `gorm:"primaryKey"`
 
@@ -63,5 +68,6 @@ func (c *Calendar) AfterFind(tx *gorm.DB) (err error) {
 		db.Raw("select name from groups where id = ?", c.GroupID).Scan(&name)
 		c.GroupName = name
 	}
+
 	return
 }
diff --git a/calendar/event.go b/calendar/event.go
index 186ba13..3569031 100644
--- a/calendar/event.go
+++ b/calendar/event.go
@@ -5,46 +5,31 @@ import (
 
 	"github.com/rs/xid"
 	"gorm.io/gorm"
-	"kumoly.io/kumoly/app/auth"
 	"kumoly.io/kumoly/app/errors"
 )
 
 type Event struct {
 	ID string `gorm:"primaryKey"`
 
-	Start       time.Time
-	End         time.Time
-	Name        string `gorm:"not null"`
-	Hosts       string
-	Description string
-	Location    string
+	Start time.Time
+	End   time.Time
+	Name  string `gorm:"not null"`
 
-	// ntu
-	Class    string
-	CourseID string
-	Semester string
+	Color string `gorm:"-"`
+
+	IsExt bool
 
 	CalendarID   string
+	EventGroup   EventGroup `json:"Detial"`
 	EventGroupID string
 
-	Group     auth.Group `json:"-"`
-	GroupName string     `gorm:"-" json:"Group"`
-	GroupID   uint       `json:"-"`
-
 	CreatedAt time.Time
 	UpdatedAt time.Time
 }
 
 func (e *Event) BeforeSave(tx *gorm.DB) (err error) {
-	if e.GroupName != "" {
-		var grp_id uint
-		db.Raw("select id from groups where name = ?", e.GroupName).Scan(&grp_id)
-		if grp_id == 0 {
-			return errors.ErrorNotFound
-		}
-		e.GroupID = grp_id
-	} else {
-		e.GroupID = 0
+	if e.CalendarID == "" {
+		return errors.ErrorBadRequest
 	}
 	return
 }
@@ -53,14 +38,16 @@ func (e *Event) BeforeCreate(tx *gorm.DB) (err error) {
 	if e.ID == "" {
 		e.ID = xid.New().String()
 	}
+	e.IsExt = false
 	return
 }
 
 func (e *Event) AfterFind(tx *gorm.DB) (err error) {
-	if e.GroupID != 0 {
-		var name string
-		db.Raw("select name from groups where id = ?", e.GroupID).Scan(&name)
-		e.GroupName = name
+	eg := EventGroup{}
+	if err := tx.First(&eg, "id = ?", e.EventGroupID).Error; err != nil {
+		return err
 	}
+	e.EventGroup = eg
+	e.Color = color[e.EventGroup.Color%len(color)]
 	return
 }
diff --git a/calendar/event_group.go b/calendar/event_group.go
index a383b97..94bb387 100644
--- a/calendar/event_group.go
+++ b/calendar/event_group.go
@@ -15,7 +15,19 @@ type EventGroup struct {
 	Name  string
 	Rrule string
 
-	Events []Event
+	// event header
+	Hosts       string
+	Description string
+	Location    string
+
+	// ntu
+	Class    string
+	CourseID string
+	Semester string
+
+	// UI
+	Color int
+	// event end
 
 	Group     auth.Group `json:"-"`
 	GroupName string     `gorm:"-" json:"Group"`
@@ -36,6 +48,8 @@ func (eg *EventGroup) BeforeSave(tx *gorm.DB) (err error) {
 	} else {
 		eg.GroupID = 0
 	}
+	eg.Color = GetNewColor(eg.GroupName)
+
 	return
 }
 func (eg *EventGroup) BeforeCreate(tx *gorm.DB) (err error) {
diff --git a/calendar/service.go b/calendar/service.go
index b969f5e..1fadbfb 100644
--- a/calendar/service.go
+++ b/calendar/service.go
@@ -1,6 +1,9 @@
 package calendar
 
 import (
+	"math/rand"
+	"time"
+
 	"kumoly.io/kumoly/app/server"
 	"kumoly.io/kumoly/app/store"
 	"kumoly.io/kumoly/app/util"
@@ -16,6 +19,7 @@ func (srv Service) Del()                      {}
 func (srv Service) Health() error             { return nil }
 
 func (srv Service) Init() error {
+	rand.Seed(time.Now().UnixNano())
 	db = store.DB
 
 	l = util.Klog.With().Str("mod", "auth").Logger()
diff --git a/calendar/util.go b/calendar/util.go
index 11f7a78..9602793 100644
--- a/calendar/util.go
+++ b/calendar/util.go
@@ -1,6 +1,8 @@
 package calendar
 
 import (
+	"math/rand"
+
 	"github.com/gin-gonic/gin"
 	"gorm.io/gorm"
 	"kumoly.io/kumoly/app/auth"
@@ -26,10 +28,10 @@ func HasEventAccess(c *gin.Context, e *Event, cid string) error {
 	if err != nil {
 		return errors.NewError(404, err)
 	}
-	if e.GroupName == "" {
+	if e.EventGroup.GroupName == "" {
 		return nil
 	}
-	if !auth.ACHas(c, auth.ADMIN, auth.SYSTEM, e.GroupName) {
+	if !auth.ACHas(c, auth.ADMIN, auth.SYSTEM, e.EventGroup.GroupName) {
 		return errors.ErrorForbidden
 	}
 	return nil
@@ -47,3 +49,13 @@ func ChangeCalGroup(tx *gorm.DB, cal_id, to string) error {
 	) where calendar_id = ?`, to, cal_id)
 	return nil
 }
+
+func GetNewColor(GroupName string) int {
+	eg := &EventGroup{}
+	if err := db.Select("color").
+		Where("group_id = (select id from groups where name = ? )", GroupName).
+		Last(eg).Error; err != nil {
+		return rand.Intn(len(color))
+	}
+	return eg.Color + 1
+}