This paper provides an investigation of the phase transition and the spalling characteristics induced during shock loading and unloading in an α phase Fe-based alloy. Two kinds of impact set-ups are used. One is referred to as the direct impact, and the other is the reverse impact. The shock Hugoniot and the release stress-volume adiabat of the α phase Fe-based alloy are obtained. And the results show that the history of loading and unloading is determined by the relationship among the phase transition threshold and the reverse transition threshold and the shock pressure. It is found that abnormal spallations happen in the α phase Fe-based alloy sample as the pressure exceeds the phase transition threshold. Such abnormal spalling phenomena are believed to be related to the shocked α→ε phase transition, and a possible reason for the abnormal spalling is discussed also from the interaction process of stress wave.