diff --git a/docs/design_docs/segcore/segment_interface.md b/docs/design_docs/segcore/segment_interface.md
index b10fcde590..6d488ed060 100644
--- a/docs/design_docs/segcore/segment_interface.md
+++ b/docs/design_docs/segcore/segment_interface.md
@@ -32,7 +32,7 @@ See design details `${milvus_root}/internal/core/src/segcore/SegmentInterface.h`
    2. SealedSegment must be 1
 7. `debug()`: debug is used to print extra information while debugging
 8. `vector_search (vec_count, query..., timestamp, bitset, output)`: Search the vector column
-   1. `vec_count`: specifies how many entities participated in the vector search calculation, the rest of the segments are filtered out because its timestamp is larger than specified timestamp. This function is mainly used in growing segment as multi version control(MVCC)
+   1. `vec_count`: specifies how many entities participated in the vector search calculation, the rest of the segments are filtered out because their timestamp is larger than specified timestamp. This function is mainly used in growing segment as multi version control(MVCC)
    2. `query...`: multiple variables jointly specify the parameters and search vector
    3. `timestamp`: timestamp is used for time traveling, filter out data with timestamp. Mainly for sealed segment
    4. `bitset`: calculated bit mask value as an output