The uniaxial tensile tests were carried out at temperature ranging from room temperature(RT)to 523 K under strain rates of 0.001,0.010 and 0.100 s-1 to obtain the flow stress of AZ31B magnesium alloy.The tensile tests were simulated by the finite element method(FEM)to calculate the critical damage values(Dc)of the Cockcroft-Latham criterion to predict the occurrence of fracture defects.Finally,the effects of temperature and strain rate on Dc were analyzed to predict the critical damage value's evolution.The results demonstrate that the critical damage value changes in the range of 0.188-0.718.It increases as strain rate decreases at constant temperature,and increases with the increase of temperature under certain strain rate,but is more sensitive to the temperature.