Based on the continuous phase field model, the precipitation behavior of Cu rich phase in Fe-Cu-Mn alloy under the action of internal magnetic energy is studied. The effects of internal magnetic energy on the average particle radius, volume fraction and Gibbs free energy of Cu rich phase at different temperatures and different Mn content and Cu content are investigated. The simulation results show that the lower the Mn content and the higher the Curie temperature, the greater the contribution of internal magnetic energy to free energy is, and the contribution of internal magnetic energy decreases with temperature increasing. The internal magnetic energy reduces the phase structure transition barrier and promotes the phase structure transition. The volume fraction of precipitated phase increases with Cu content increasing. Compared with the effect of internal magnetic energy on the volume fraction of precipitated phase, the effect of internal magnetic energy leads to a large volume fraction of precipitated phase. Therefore, under the action of internal magnetic energy, the Cu rich phase has larger average particle size, volume fraction and smaller coercivity. Finally, the change trend of alloy hardness is predicted.