Abstract: ER5087 aluminum alloy wires were cladded on a 6082-T6 aluminum alloy plate by double pulse melting inert gas shielded welding for four passes, and specimens were taken at different positions in the welding heat affected zone (HAZ) for microstructure observation and mechanical property tests. Combined with numerical simulation of welding temperature field, the effect of multiple welding thermal cycling on the microstructure and mechanical properties at different positions in the HAZ were studied. The results show that based on tested hardness variation and simulated peak temperature variation of the cross section of the HAZ, combining with material heat treatment process, the HAZ of 6082-T6 aluminum alloy welded joint was divided into a over-aged zone (zone A), a severely over-aged zone (zone B), and a solid solution zone (zone C) according to the distance ( from far to near) from fusion line. With the increase of welding pass, the grain size of the HAZ became coarser; the precipitated phase in zone A changed from β″ phase+β' phase→β' phase+U2 phase→β phase+β' phase+semi-dissolved phase→β' phase+semi-dissolved phase. After different-pass welding, the precipitated phase in zone B was basically in semi-dissolved state, and the ordered precipitated phase in zone C was completely dissolved and only a large amount of GP zones existed. With the increase of welding pass, the precipitated phase in zone A and zone B of the HAZ was coarsened and dissolved gradually, and the number of GP zones in zone C decreased. After four-pass welding, the overall mechanical properties of the HAZ decreased, and the softening in zone B of the HAZ was the most serious. The main reason for softening of HAZ was the evolution of precipitated phases rather than grain coarsening.