diff --git a/pkg/master/README.md b/pkg/master/README.md
index 01c1caeb84..30aca7743c 100644
--- a/pkg/master/README.md
+++ b/pkg/master/README.md
@@ -11,3 +11,14 @@ go run cmd/master.go
 ```
 
 ## Start with docker
+
+
+## What rules does master use to write data to kv storage?
+1.find the root path variable ```ETCD_ROOT_PATH ```which defined in common/config.go 
+2.add prefix path ```segment``` if the resource is a segement
+3.add prefix path ```collection``` if the resource is a collection
+4.add resource uuid
+
+### example
+if master create a collection with uuid  ```46e468ee-b34a-419d-85ed-80c56bfa4e90```
+the corresponding key in etcd is /$(ETCD_ROOT_PATH)/collection/46e468ee-b34a-419d-85ed-80c56bfa4e90
diff --git a/pkg/master/mock/segment.go b/pkg/master/mock/segment.go
index 59bf1c66c7..65bfa3a9b9 100644
--- a/pkg/master/mock/segment.go
+++ b/pkg/master/mock/segment.go
@@ -35,19 +35,19 @@ func SegmentUnMarshal(data []byte) (SegmentStats, error) {
 }
 
 type Segment struct {
-	SegmentID      uint64     `json:"segment_id"`
-	Collection     Collection `json:"collection"`
-	PartitionTag   string     `json:"partition_tag"`
-	ChannelStart   int        `json:"channel_start"`
-	ChannelEnd     int        `json:"channel_end"`
-	OpenTimeStamp  uint64     `json:"open_timestamp"`
-	CloseTimeStamp uint64     `json:"close_timestamp"`
+	SegmentID      uint64 `json:"segment_id"`
+	CollectionID   uint64 `json:"collection_id"`
+	PartitionTag   string `json:"partition_tag"`
+	ChannelStart   int    `json:"channel_start"`
+	ChannelEnd     int    `json:"channel_end"`
+	OpenTimeStamp  uint64 `json:"open_timestamp"`
+	CloseTimeStamp uint64 `json:"close_timestamp"`
 }
 
-func NewSegment(id uuid.UUID, collection Collection, ptag string, chStart int, chEnd int, openTime time.Time, closeTime time.Time) Segment {
+func NewSegment(id uuid.UUID, collectioID uuid.UUID, ptag string, chStart int, chEnd int, openTime time.Time, closeTime time.Time) Segment {
 	return Segment{
 		SegmentID:      uint64(id.ID()),
-		Collection:     collection,
+		CollectionID:   uint64(id.ID()),
 		PartitionTag:   ptag,
 		ChannelStart:   chStart,
 		ChannelEnd:     chEnd,
diff --git a/pkg/master/mock/segment_test.go b/pkg/master/mock/segment_test.go
index 610b93aff5..0ad2030469 100644
--- a/pkg/master/mock/segment_test.go
+++ b/pkg/master/mock/segment_test.go
@@ -30,14 +30,8 @@ func TestSegmentMarshal(t *testing.T) {
 }
 
 var Ts = Segment{
-	SegmentID: uint64(101111),
-	Collection: Collection{
-		ID:            uint64(11111),
-		Name:          "test-collection",
-		CreateTime:    uint64(time.Now().Unix()),
-		SegmentIDs:    []uint64{uint64(10111)},
-		PartitionTags: []string{"default"},
-	},
+	SegmentID:      uint64(101111),
+	CollectionID:   uint64(12010101),
 	PartitionTag:   "default",
 	ChannelStart:   1,
 	ChannelEnd:     100,
diff --git a/pkg/master/server.go b/pkg/master/server.go
index 2469015fd5..27024b0db6 100644
--- a/pkg/master/server.go
+++ b/pkg/master/server.go
@@ -129,7 +129,7 @@ func CollectionController(ch chan *messagepb.Mapping) {
 			time.Now(), fieldMetas, []uuid.UUID{sID},
 			[]string{"default"})
 		cm := mock.GrpcMarshal(&c)
-		s := mock.NewSegment(sID, c, "default", 0, 100, time.Now(), time.Unix(1<<36-1, 0))
+		s := mock.NewSegment(sID, cID, "default", 0, 100, time.Now(), time.Unix(1<<36-1, 0))
 		collectionData, _ := mock.Collection2JSON(*cm)
 		segmentData, err := mock.Segment2JSON(s)
 		if err != nil {