Objective To investigate the mechanism of CO2 corrosion resistance of Ni-Fe-P coating. Methods By means of SEM,EDS,XRD and EIS, CO2 corrosion resistance behavior at the surface of 35CrMo with Ni-Fe-P coating was characterized and analyzed. Results The results showed that after Ni-Fe-P coating, the surface of 35CrMo was turned into amorphous microstructure and its hardness reached up to 570. 12HV. The polarization resistance increased and the corrosion tendency decreased, which provided good protection for the matrix. During the corrosion process, the corrosion behavior of the coating was affected by electric double layer capacitance and passivated film. Conclusion The Ni-Fe-P coating could significantly improve the resistance to CO2 due to its great passivation tendency in CO2 solution.