The effect of ocean acidification on shellfish was a long–term process, however, the water pH can be changed rapidly in aquaculture. Therefore, the study of physiological responses of shellfish in different sizes under different pH stress would be with significatively value in the aquaculture. In this study, we used the blood clam (Tegillarca granosa) with different sizes (9.12 mm, 22.38 mm and 32.35 mm) as a model to explore the effects of feeding physiology under different pH (6.5﹣9.5) stress (Table 1). Clearance rate, ingestion rate and absorption efficiency were determined in static bioassay tests, which were used to represent the feeding physiology of the mud clam. At pH = 8.5, the clearance rates from high to low were as follows: large > medium > small (Fig. 1); the ingestion rates from high to low were as follows: medium, large, small (Fig. 2); and the absorption efficiencies from high to low as follows: medium > small > large (Fig. 3). Although the large blood clam had the highest Clearance rate, the medium blood clam had higher ingestion and absorption capacity. The clearance rate, ingestion rate and absorption efficiency of blood clam were related to pH and its size (P < 0.05) by two–way ANOVA. The influence of pH on the clearance rates were as follows: small (P < 0.05) < medium (reference) < large (P > 0.05) (Fig. 1); the influence of ingestion rates were as follows: large (P > 0.05) < small (reference) < medium (P < 0.05) (Fig. 2); and the influence of absorption rates were as follows: small (P > 0.05) < medium (reference) < large (P < 0.05) (Fig. 3). The Ingestion rate of medium blood clam was greatly affected by the environmental pH, and the absorption efficiency of large blood clam was greatly affected by the environmental pH.