Sinonovacula constricta was used as the research species. Acute low salinity stress method was used, and the survival rate, Na⁺/K⁺-ATPase (NKA) activity and phagocytosis of hemocytes of S. constricta were measured. The results showed when the salinity was set from 8 to 2, the survival rate of three different sizes S. constricta were almost 100%, the NKA activity kept relatively stable, and the phagocytic capacity of hemocytes only had a small range of decline. When salinity was set from 2 to 0, the survival rate of three different sizes S. constricta decreased with the decrease of salinity, and the survival rate of adult was higher than that of the sub-adult and juvenile all the time. The NKA activity was correspondingly increased to maintain the osmolality balance inside and outside of the body. It is believed that the physiological function of S. constricta was affected by salinity acute decrease, so the phagocytic capacity of hemocytes was reduced. The low salinity LC₅₀ of juveniles, sub-adults and adult were 1.45, 1.25 and 0.75, respectively. In summary, S. constricta has a strong tolerance to acute low salinity and could be a potential inland aquaculture species.