In order to study the effects of changing temperature condition on solid rocket motor, the thermal stress of solid rocket motor under temperature cycling and temperature shock was analyzed. The cumulative damage model of HTPB propellant grain was built and the cumulative damage of this grain under temperature changing condition was computed. The results indicate that, the damage degree increases with the strictness of environments. The damage under temperature shock was greater than that of under temperature cycling. Under temperature shock condition, the cumulative damage of grain was influenced by temperature range and parameters of propellant, and the effect of equilibrium modulus of propellant on cumulative damage was as same as the effect of expansion coefficient. The results can afford available reference for research on properties of HTPB propellant in storage and use.