After 5 days experimental exposure of Meretrix meretrix to different dosage of cadmium solution(0、1.5mg/L、3mg/L、6mg/L), the ultrastructural changes of hepatopancreas cells of M. meretrix was observed using transmission electron microscopy. The results showed that acute cadmium poisoning made a remarkable changes of the ultrastructure of hepatopancreas cells of M. meretrix, mainly in the breakage of endomembrane system and mitochondrial. The mitochondrial became swelling and vacuolating gradually, some mitochondrial crisae disintegrated. Rough endoplasmic reticulum ( RER ) disintegrated from the original plate layered, and formed in many different sizes of vesicles. Microvilli broke off and decreased gradually, and the vacuole appeared. Cytoplasm swelled and formed vacuoles which was filled with some sediment. The nuclear membrane invaginated and the membrane of golgi apparatus expanded too. The structural of the most organelles and endomembrane system were destroyed by Cd₂ solution, that affected the normal physiological function of hepatopancreas cells. With the increased concentration of cadmium solution, the cells of hepatopancreas also enhance the destruction.