With a view to successfully forming multi-sheet cylinder sandwich structure of Inconel718 superalloy, high temperature plasticity of the laser butt welding plate for Inconel718 superalloy with ultra-fine grain was studied in this paper.The experiment results show that tensile direction has great effect on elongation of laser welding butt plate.When the tensile direction is vertical to laser welding seam, maximum elongation reaches 458.56% at temperature of 950℃ and strain rate of 3.l × 10-4s-l, in which value of m is 0.352 and welding seam is not deformed.When the tensile direction is parallel to laser welding seam, the maximum elongation is 178.96% at 965℃ with strain rate of 6.2×10-4s-1.Value of m is 0.261, and welding seam contributes to the deformation.In the experiment, with tensile direction vertical to laser welding seam, values of m are higher than 0.3 and welding seams are not deformed.Whereas, with tensile direction paralled to laser welding, welding seams are parts of the deformation and values of m are less than 0.3.Before welding seam is stretched, microstructure in the center is fine equiaxed dendrite, and at the edge is columnar crystal.Meanwhile, there is Laves phase with high content Nb precipitated in the welding seam.After stretch in the vertical direction, dendrite in the welding seam grows.However, a mixed microstructure with dendrite and equiaxed crystal appeared in welding seam due to dynamic recrystallization when tensile direction paralleled to welding seam.After tensile deformation, there is δ phase transformed from laves phase, with a small part of residual laves phase in welding seam, while, in base material, cavities appeared in grain boundary of the equiaxed crystal.The laser butt welding plate of Inconel718 superalloy deforms perfectly at 965℃,and deformation of Multi-sheet cylinder sandwich structure verifies that laser butt welding plate of Inconel718 superalloy can meet the requirements of superplastic forming.