Thermalstress numerical simulation was carried out on solid propellant motor under the load of low temperature or temperature periodic variation environment temperature in order to investigate the temperature effect. The temperature fields and the stress-strain responds were obtained. It is shown that the maximal thermal stress appears at the interface of shell and insulator under low temperature, and it is the dangerous area of the solid motor caused by thermal stress. The maximal strain appears at the inside boundary of the motor grain, where is the dangerous place caused crack. Under the load of temperature periodic variation, the maximal thermal stress appears at 0. 346m away from the inside boundary, it is the dangerous area of the grain to be apart.