This paper provides an investigation of the phase transition and spalling characteristic induced during shock loading and unloading in the pure iron and the FeMnNi alloy.The impact for the pure iron is symmetric and with the same-thickness for both the flyer and the target plate.It is found that an abnormal multiple spalling happens in the pure iron sample as the pressure exceeds the αε transition threshold of 13 GPa.In the symmetric and same-thickness impact and reverse impact experiments of the FeMnNi alloy,two abnormal tension regions occur when the pressure exceeds the αε transition threshold of 6.3 GPa,and the reverse phase transition εα begins below 4.2 GP.The experimental process is simulated successfully from the non-equilibrium mixture phase and Boettger’s model.Such abnormal spalling phenomena are believed to relate to the shocked αε phase transition.The possible reasons for the abnormal multiple spalling,which occurs during the symmetric and same-thickness impact experiments of pure iron and FeMnNi alloy,are discussed. This paper provides an investigation of the phase transition and spalling characteristic induced during shock loading and unloading in the pure iron and the FeMnNi alloy. Impact for the pure iron is symmetric and with the same-thickness for both the flyer and the target plate. The is found that an abnormal multiple spalling happens in the pure iron sample as the pressure exceeds the alpha ε transition threshold of 13 GPa. The symmetric and same-thickness impact and reverse impact experiments of the FeMnNi alloy, two abnormal tension regions occur when the pressure exceeds the αε transition threshold of 6.3 GPa, and the reverse phase transition εα begins below 4.2 GP. The experimental process is simulated successfully from the non-equilibrium mixture phase and Boettger’s model. phase transition. The possible reasons for the abnormal multiple spalling, which occurs during the symmetric and same-thickness impact exp eriments of pure iron and FeMnNi alloy, are discussed.