Abstract: Aiming at the problems that it is difficult to evaluate the structural strength and fatigue life of a full-scale solid rocket motor (full-scale SRM) under random vibration loads via random vibration tests during development, and that conducting impact tests using the full-scale SRMs entails high cost and risks, this paper establishes an equivalent simulation design method for subscale SRM and full-scale SRM under vibration and impact loads based on the second similarity theorem and dimensional analysis. Meanwhile, equivalent calculation methods for power spectral density and equivalent height were proposed. The finite element numerical simulation method was adopted to verify the modal frequencies, vibration modes, structural responses of subscale and full-scale SRM under vibration and impact loads. The results show that: the maximum error in the natural frequency prediction of the full-scale SRM using the subscale SRM is 0.32%; the modal shapes at each order are highly consistent between the two models; the frequency response of the subscale SRM, after conversion using the similarity coefficient, is basically consistent with that of the full-scale SRM. In addition, under equivalent random vibration loads, the root-mean-square equivalent stress and strain of the subscale SRM are 0.029 MPa and 0.25%, respectively, while those of the full-scale SRM are 0.023 MPa and 0.19%, with similar calculation results. Under equivalent impact loads, the equivalent stresses of the subscale and full-scale SRM are 2.53 MPa and 2.55 MPa, respectively, and the equivalent strains are 10.81% and 10.89%, respectively. This demonstrates that the subscale SRM can be used to predict the natural frequencies, modal shapes, structural frequency responses, random vibration responses, fatigue life and structural responses under impact loads of full-scale SRM, thereby significantly reducing the development cost, cycle, and risks of SRMs.