diff --git a/be/src/olap/field.h b/be/src/olap/field.h
index 1b421efc4e8127..aaaf5cf063cae3 100644
--- a/be/src/olap/field.h
+++ b/be/src/olap/field.h
@@ -162,16 +162,11 @@ inline int Field::index_cmp(char* left, char* right) const {
             // l_slice size and r_slice size may be less than compare_size
             // so calculate the min of the three size as new compare_size
             compare_size = std::min(std::min(compare_size, (int)l_slice->size), (int)r_slice->size);
+
+            // This functionn is used to compare prefix index.
+            // Only the fixed length of prefix index should be compared.
+            // If r_slice->size > l_slice->size, igonre the extra parts directly.
             res = strncmp(l_slice->data, r_slice->data, compare_size);
-            if (res == 0) {
-                if (l_slice->size < r_slice->size) {
-                    res = -1;
-                } else if (l_slice->size > r_slice->size) {
-                    res = 1;
-                } else {
-                    res = 0;
-                }
-            }
         } else {
             res = l_slice->compare(*r_slice);
         }