Abstract: In order to study the cause of molting death of Procambarus clarkii and its preventive measures, we raised and stressed the crayfish of different sizes by different environmental factors. The results show that the survival rate and decidua rate of P. clarkii were highest in groups of 30 mg·L⁻¹ Ca²⁺ and 15 mg·L⁻¹ Mg²⁺, significantly higher than those in the contol (P<0.05), but their decidua mortalities were significantly lower than those in the control (P<0.05). When the pH value was 9.23 or the dissolved oxygen concentration was 4.5 mg·L⁻¹, the survival rate and decidua rate were significantly lower than those in the control (P<0.05), but the decidua mortality was significantly higher than that in the control (P<0.05). The molting mortality of P. clarkii was highest when the salinity was 21 (P<0.05). Environmental factors and many other factors are the important causes of molting death of P. clarkii.