Quinary phase-field model was extended and constructed, and the diffusion-controlled phase decomposition and morphology in thermal aging Fe-Cu-Mn-Ni-Al quinary system coupled with CALPHAD thermodynamic databases were successfully studied. The effects of Manganese composition on the morphology, volume fraction, number density, particles size and growth and coarsening of Cu-rich precipitates were investigated systematically. The simulation results showed that Cu-rich phase was firstly formed, and the Ni, Al and Mn atoms were partitioned to the Cu-rich phase, leading to the formation of a Ni-Al-Mn-rich intermetallic ring/Cu-rich core precipitate morphology and final conversion of Cu-rich phase to Cu-rich phase. The curves of volume fraction and free energy variation with simulation time indicated that Mn element can promote nucleation driving force to overcome the nucleation barrier in initial stage and can also accelerate the precipitation of Cu-rich phase and promote the growth and coarsening processes. Through the analysis of number density (ND) and average particle size (APS), we found that the values of ND and APS of Cu-rich particles increase with the rising of Mn content, which indicates that the higher Mn content will boost the nucleation and growth rate. Moreover, the time exponent at the later precipitation was 0.41, 0.42 and 0.37, respectively, which had deviations with the 0.33 of the LSW's value, and the growth and coarsening of Cu-rich precipitates were under the mixed mechanisms of Ostwald ripening and coalescence coarsening of neighboring precipitates. These results provided useful information for the preparation of multi-component alloyed steel with excellent mechanical properties to some extent.