Abstract: The Chinese mitten crab (Eriocheir sinensis) is often caused by hypoxia to impact growth and immunity. E. sinensis tremor disease is caused by the pathogen Spiroplasma eriocheiris, which is highly contagious with a high mortality rate. To explore the effect of hypoxia stress and the S. eriocheiris infection on E. sinensis, the mortality rate and the histopathology of crab, the Spiroplasma copy number, apoptosis & necrosis and mitochondrial membrane potential in hemocytes were studied. The results showed that long-term hypoxia stress damaged hepatopancreas and gill tissues. Multiple vesicles appeared in the crab hepatopancreas after 8d hypoxic stress. The crab gill tissue was diffused after 8d hypoxia stress. The mortality of E. sinensis in hypoxia group under S. eriocheiris infection at 10d was 100%, meanwhile, the mortalities in normoxia group under S. eriocheiris infection at 10d and 12d were 50% and 70%, respectively. The mortality of E. sinensis in hypoxia group at day 12 (60%) was higher than the mortality in normoxia group (30%). These results reveal that the hypoxia could accelerate the crab dead under S. eriocheiris infection with increased copy number of S. eriocheiris in hemocytes and enhanced hemocytes necrosis rate (PI stain) and apoptosis rate (FITC/PI stain). Hypoxia increased the mitochondrial membrane potential in hemocytes under S. eriocheiris infection at 4d, 6d and 8d, and S. eriocheiris infection induced the mitochondrial membrane potential in hemocytes. These results indicate that hypoxia stress and S. eriocheiris infection have a synergistic harmful effects on the physiology and biochemistry of E. sinensis.