Dissimilar metals of 1060 aluminum and galvanized steel were joined with lap joint by pulsed double electrode gas metal arc welding-brazing with ER4043 aluminum filler metals. The welding joints of aluminum and steel were heat-treated at 270 ℃ and 350 ℃. The microstructure of the welded joint was observed by scanning electron microscopy,the diffusion and hardness distribution of alloying elements in different areas of the welded joint before and after heat treatment were tested by energy spectrometer and microhardness tester. The results show that the homogenization diffusion of alloy elements in welding joint occurs after heat treatment.After heat treatment at 350 ℃,a layer of Fe,2,Al,5,Zn,0.4, intermetallic compound was formed in the weld toe area of the welding joint. The microhardness distribution of weld metal is uniform and the change of microhardness of weld toe area is smaller after heat treatment at 270 ℃,it is beneficial to avoid the stress concentration and improve the mechanical properties of the welding joint.