In order to study the Effects of quenching on the microstructure and properties of AS300/MBW500 unequal-thickness laser wire-filled welded joints, experiment of water quenching heat treatment on the basis of AS300/MBW500 unequal thickness steel laser wire filling welding. By analyzing the microstructure, Vickers hardness and element composition of the welded joint, the effect of water quenching heat treatment on the performance of the welded joint is obtained. As the quenching temperature increases, the accumulation of Al elements in welded joints increases and the hardness of weld decreases. When 930 ℃, the hardness step value between sheet and weld, weld and thick plate is equal, the tensile strength of weld is 908 MPa, the elongation is 7.5%, which increases the mechanical properties of laser wire filling welded of unequal thickness steel.