Based on the Microscropic Phase-field method and the interatomic potential equation, we calculate the first near-neighbor interatomic potentials of the L10 structure in Co-Pt alloy, and the results show that the first near-neighbor interatomic potential of the L10 structure in the Co-Pt alloy increases with temperature, and increases with concentration. The first near-neighbor interatomic potential, which linearly changes with the temperature and concentration, is close to other literature result. Using the interatomic potential to simulate the Co-Pt alloy precipitation process and the final morphology, the simulation results can get L10 and L12 structure. According to the sequence parameters, we can get that the L10 structure precipitation mechanism characteristics are spinodal decomposition, and then coarsed. The final two-phase volume fraction is close and the alloy precipitation profile and experimental results are consistent. The calculation of the interatomic potential for L10 structure in Co-Pt alloy using Phase-field method can expand the application range of Phase-field method in alloy design with L10 structure.