To improve the microstructures and corrosion resistance of Ni-based cladding coatings, the crack free Ni-based coatings were prepared by laser cladding technology, and then were treated by ultrasonic impact. The microstructure and corrosion resistance of cladding coating and impact hardening layer were studied by scanning electron microscope (SEM), electron probe microanalysis (EPMA) and electrochemical equipment, and the hardening mechanism of Ni-based cladding coating by ultrasonic impact treatment was analyzed. The results show that the laser cladding Ni-based coating was mainly composed of γ-(Fe,Ni) solid solution and carbides along grain boundary. The microstructure of laser cladding Ni-based coating was composed of cellular dendrite and fine dendrite from the bottom to top region. In addition, the Cr content at the grain boundaries in cladding coating was higher than that at grain boundaries while the Cr content intragranular at upper region was higher than at the bottom and middle regions. Ultrasonic impact treatment does not change the phase composition of Ni-based cladding coating, but on the surface of which a fine grain layer with a thickness of 5 μm was formed. The carbides distributed along the grain boundaries in the impact hardening layer were broken into fine carbides and dispersed inside the grains, which played the role of fine grain strengthening and dispersion strengthening. After ultrasonic impact treatment, the surface roughness decreased from 0.52 μm to 0.29 μm, and the surface hardness increased by more than 50%. The general self-corrosion potential of impact hardened layer increased by 37.21 mV, and the general self-corrosion current density decreased by 57.9%, while the corrosion surface was even and smooth with many fine carbides dispersed. Therefore, ultrasonic impact treatment could refine the microstructures of laser cladding Ni-based coating, and the corrosion resistance of which was improved obviously.