Abstract: In order to alleviate the softening problem of 6N01 aluminum alloy during fusion welding, the microstructure and mechanical properties of MIG welded joints with water accelerated cooling were studied and compared with the joints under natural cooling conditions. The results of metallographic experiments showed that the partially melted zones of filling pass and cover pass were narrowed by water cooling. The columnar grain regions of the weld near the fusion line were widened and the equiaxed grains in the weld were refined. Microhardness test results showed that the softening zone of the joint was significantly narrowed and the hardness increased under water cooling conditions. The TEM morphology of the softened zone showed that the sizes of β' precipitation were also reduced. The yield strengths and tensile strengths of MIG welded joints were also improved by water cooling. The experimental results confirmed that water cooling can optimize the microstructure and improve the mechanical properties of MIG welded 6N01 aluminum alloy joints.