In this paper, cold metal transfer + pulse welding (CMT+P) method was used to weld 7A52 aluminum alloy, and the effects of different heat treatment processes on the microstructure and mechanical properties of welded joints were studied. The results show that the microstructure dominated by dendrite or equiaxed dendrite in the weld zone has transformed into equiaxed crystal after heat treatment, but the grain structure and the size of the second phase of AA(Artificial Aging) sample are coarser, and there is segregation at the grain boundary. The amount of precipitates in T6(Solid Solution + Artificial Aging) weld zone is more than AA, and the size of η′(MgZn2) strengthening phase and the width of precipitation free zone is decreased in the heat affected zone. The joint strength of AA and T6 samples reached 315 MPa and 356 MPa respectively. AA has limited improvement on the mechanical properties of the joint, while T6 has increased by about 14.10% compared with AW. The micro fracture of AA sample is mainly dimple transgranular fracture, while the number of dimples in the fracture of T6 sample is significantly reduced and replaced by an uncharacteristic platform. At this time, the joint is mainly transgranular + intergranular ductile brittle mixed fracture.