The distribution pattern of Bullacta exarata was studied in different seasons of 2004 at south shore of Hangzhou Bay, China. We found that the distribution pattern of B. exarata was aggregated in each season by Taylor's power regression and Iwao's plot regresses methods (P < 0.001). Based on two-way ANOVA analysis, the results indicated that the densities were significantly affected by the factors of season (P < 0.001), distance to the dyked dam (P < 0.001) and the interaction between them (P < 0.001). The densities distribution followed with the distance gradient was significantly different in each season with one-way ANOVA analysis. The results of Pearson correlation coefficients analysis on data of density indicated that in the warmer seasons (spring and summer) the highest densities occurred at 150 m to the dyked dam, while in the cooler seasons peak in densities were at 250 m to the dyked dam (autumn and winter). In the study area, seasonal variation of B. exarata densities should be the response of the species to the environmental change, especially the food resource.