Abstract: Spawning ground, the reproduction place of fish, is an important and susceptive habitat. Weighted usable area has been widely used in evaluating the suitability of spawning ground. However, previous studies on the diversity of spawning ground were very rare. To describe the impact caused by the change in river discharge, a concept of microhabitat heterogeneity is presented in this paper based on the habitat heterogeneity in landscape ecology. Water depth and velocity patches were chosen as two major factors in evaluating the heterogeneous level of microhabitat and the Shannon diversity index was adopted as a mathematic principle. A case study of the Fuxing village downstream of the Jinchuan dam on the Dadu River was taken to identify the relationship of microhabitat heterogeneity versus river discharge. According to the results, the optimum flow depth-velocity heterogeneity occurs at the discharge of 156 m3/s.