In this study, an influence of the front steel plate of the steel-plate concrete (SC) composite walls on the impact resistance performance is analytically derived, and verified by comparison with numerical analyses and experiment results. SC composite wall is remarkably superior in resistance against impacts compared to normal concrete because steel plates control and prevent fragmentation caused by the fracture of concrete material. An analytical criterion for estimating resistance capacity against impact loads is proposed by adding the effect of a front steel plate into the existing impact resistance equation of SC composite walls, and the criterion more accurately predicts the failure modes of SC composite walls in the impact tests. Finite element (FE) models are constructed to predict the impact response of SC composite walls numerically and verified with experiment results. The critical velocity is numerically derived using FE models by performing a large number of iterative simulations, and the proposed criterion including the effect of front steel plate is more accurate for estimating critical velocity than the formula that ignores the front steel plate. The proposed analytical and numerical procedures will be useful for assessing the critical velocities and failure modes of SC composite walls with better accuracy.