Fe-Cr alloys have become candidate materials for the internal devices of the fourth-generation nuclear reactor due to their excellent properties. However, they face the risk of hardening and embrittlement in an environment of high temperature and high radiation for a long time. This may be due to changes in microstructure, such as α-α‘ phase transition. Therefore, it is of great significance to study the phase transformation process of Fe-Cr alloy. In this work, we consider the effect of vacancies on the properties of the alloy and use molecular dynamics (MD) simulations to calculate the interaction energy between different atoms in the Fe-Cr alloy. Then, we carry out a Monte Carlo (MC) simulation of the α-α‘ phase transformation process of the Fe-Cr alloy, which has an important reference value for optimizing the properties of the alloy.