Abstract: This article obtained the loading and unloading process and phase transition spalling characteristics of FeMnNi alloy through symmetrical and same thickness impact and reverse impact experiments. By means of the modified Boettger model and a non-equilibrium mixture phase model, we explained the physical principle of the shock phase transition and reverse transition and rarefaction shock wave in numerical simulation. We described the spalling mechanism from the interaction process of stress wave. And we found that the phase transition and reverse transition of FeMnNi alloy sample are just about the physical mechanism which leads to spallation.