An enclosure experiment was carried out to investigate the quantitative proportion and stocking density of clam Tegillarca granosa in polyculture with Pacific white-leg shrimp Litopenaeus vannamei to optimize the polyculture. In the ratio optimization trial, the clam was reared respectively at stocking density of 750, 1150 and 2250 kg/hm2, and the shrimp density was 1.7×104 ind/hm2 in all groups, with the quantitative clam-shrimp ratios being 1.84 (A), 2.75 (B) and 5.50 (C). While in the stocking density trial, under the optimized ratio of clam to shrimp (4:1), the clam was reared at the stocking density of 50 (L), 75 (M), and 100 (H) ind/m2 respectively. Results showed that NH3-N concentration of Group B was significantly lower than that of Group A (P<0.05) and the nitrate of Group A was significantly lower than that of Group B (P<0.05); no significant differences were found in other water indexes (P>0.05). The shrimp yield of Group B was significantly higher than Group A (P<0.05), and the earnings rates were significantly different (P<0.05) with Group B > Group A > Group C in proper sequence. In the density trial, the SGR, survival rate and growth rate of clams in Group M were all higher than those of Group L and H; no significant differences in chemistry indexes of water were found among the groups during the experiment. The research showed that the polyculture system was optimized with the clam-shrimp ratio of 4:1 and the clam density of 75 ind/m2.