To address the ground ambient temperature storage and prolonged high-low temperature cycling caused by temperature control system malfunctions during the actual service of large solid rocket motors, an equivalent simulation design method for scaled-down solid rocket motors under temperature cycle loads was established based on the second similarity theorem and dimensional analysis. The finite element numerical simulation method was used to verify the structural responses of the scaled-down motor and the prototype motor under temperature cycle loads. The results show that, under equivalent temperature cycle loads, the magnitude and distribution of the equivalent stress and equivalent strain of the propellant grain in the scaled-down motor are completely consistent with those in the prototype motor. This proves that the small-sized, low-cost scaled-down motor can be used to equivalently simulate the effects of temperature loads on the propellant grain of large-sized prototype solid rocket motors, potentially significantly reducing the development cost, cycle, and expenses of the motors.