Abstract: The formation process and separation of the explosive formed projectile (EFP) formed by triple-layer tandem EFP were investigated based on numerical simulation, by which the formation process of triple-layer tandem EFP was described and the influence principle of different liner materials on the separation of triple-layer EFP was also revealed. The simulation results indicate that the formation process of triple-layer EFP consisted of impact phase, closing phase and free fight phase. In the impact phase, kinetic energy exchange mainly occurred during the axial impact of triple-layer liners, producing velocity difference in the axial direction, which was the main reason for the separation of triple-layer EFP. In the closing phrase, triple-layer liners stretched and closed gradually while impacting with each other in the axial and radial direction, which further affected the formation process and separation of triple-layer liners. In the free flight phase, the velocity and appearance of triple-layer EFP tended to be stable and the impact no longer existed, and distance between the three EFPs became larger as time progressed. In addition, different liner materials had an importance influence on the separation of triple-layer EFP, the 45#steel liner not only achieved fast separation from the front copper liner, but also effectively obstructed the separation from the following copper liner. Further numerical simulation results show a good agreement with the X-ray experiment results, which demonstrates the efficiency of the numerical simulation.