Objective To study the influence of defocusing amount on the forming quality of the cladding layer during the laser cladding process. Methods When the speed was kept constant at 2 mm/ s and the voltage was 8 V, the influence of different defocusing amount on cladding size, Rockwell hardness, interface microhardness and microstructure was comparatively analyzed by changing the distance between the head of cladding and the substrate as well as the laser power. The optimal defocus amount was determined. Results The surface hardness of the cladding layer first increased gradually and then tended to be stable, and Rockwell hardness reached up to 55 ~56HRC when the defocusing amount was 3 mm or 4 mm. Since the defocus amount was too large, the metallurgical bonding between the substrate and the cladding layer was weak, and part of the powder was not fully melted and attached to the cladding layer surface, so that the quality of cladding was poor when the defocusing amount was 5 mm or 6 mm. Under constant power, the cladding layer width decreased with the increasing defocusing amount. When the defocusing amount was 3 mm, the maximum cooling rate was achieved, and columnar crystals were most likely to grow along the melt radiating, leading to the formation of equiaxed crystal structure on top of the cladding layer. Conclusion Defocusing amount is one of the important process parameters in laser cladding. The finally optimized process parameters were v = 2 mm / s,U = 8 V,P = 1200 W,DL = 3 mm.