Abstract: High temperature tensile test was used to investigate the superplastic deformation behavior of laser weld joint.Microstructure evolution principles of weld bead and HAZ during superplastic deformation were analyzed.Equiaxial rate was introduced to characterize the microstructure transition extent of weld bead, and average grain size was introduced to characterize the microstructure transition extent of HAZ.The results indicated that equiaxial rate increased with straining, and with forming temperature increasing.It also increased with strain rate decreasing.Average grain size increased with straining, and with forming temperature increasing.