Abstract: From the view of practical point, the welding tests of HT250 and Q235 dissimilar metals were carried out by adopting the lowest cost, simplest oxygen-acetylene flame brazing welding method with φ2.5 mm BCu54Zn copper-base brazing alloy as the intermediate layer, and the metal composite plate with high impact toughness and hardness was obtained. The microhardness, metallographic microstructure and impact toughness of the metal composite plate before and after the heat treatment were tested. The results show that the pre-weld carbon removal treatment of the gray cast iron welding surface can avoid insufficient bonding defect of the brazed joint caused by the high carbon content of gray cast iron. After three times of decarburization treatment on the surface, the bonding between the weld seam and the plate is better, the brazing material spreads smoothly and evenly, and the impact toughness is higher, which is 57.4 J/cm2. The surface hardness of the weldment after quenching treatment is the highest, which can reach up to 418.2 HV.