Numerical simulation of temperature field and thermal stress field in die casting die for Al alloy wheel was performed by the Procast software in practical product.The position often encountered in crack in practical aluminum alloy wheel was simulated by the software to obtain different variation of thermal stress field with different processing parameters.The optimized processing parameters were presented.The results show that with increasing in pouring temperature,surface thermal stress in crack position at the die is increased.However,with increasing in pre-heating temperature of the die and decreasing in temperature gradient in the die surface,it is decreased.