This study aimed to investigate the interference of explosive reactive armor (ERA) on the penetration capability of explosively formed projectiles (EFPs). A numerical simulation model of EFP and the ERA interaction system was established. Flash X-ray experiments for observing the interaction between EFP and ERA were performed. It turned out that the simulation method and material model was valid. From the numerical simulation, the residual depth of penetration (RDOP) of EFPs with different materials, scales, and shapes at several angles was evaluated, and the mechanism of ERA interference EFP was revealed. The results suggested that after an EFP passed through an ERA, its RDOP to target decreased with an increase in the angle and explosive layer thickness. The higher the density of EFP is, the stronger the resistance ability of EFP to ERA is. For copper EFPs, in the EFP charge diameter range of 90mm to 170mm, each 10-mm growth in the EFP charge diameter results in an approximately 0.025 P-0 increment in RDOP (P-0 is penetration depth of EFP without ERA interference). Moreover, in the condition of the same mass, for each increase of 1 in the aspect ratio of the EFP, the RDOP increased by approximately 0.05 P-0. In addition, calculation models for the RDOP, considering the charge diameter and EFP shape, were established respectively.