The isothermal stamping process of hemisphere shell for the large-size TA7ELI helium cylinder used for future launch vehicles had been researched in this work. The isothermal stamping process of hemisphere shell was simulated by finite element analysis software before a forming process， the influence of the process on the material properties was investigated by comparing the changes of the material microstructure and mechanical properties before and after the forming. Experimental result indicates that during isothermal stamping， the stress and strain of the material gradually extends from the core to the edge， the applied load reaches the maximum value when the forming process operates later period. Furthermore， the thinnest position of the hemisphere shell is around the center of the ball bottom. The grain morphology and size of TA7ELI material changes little after stamping， and the strength of the shell at room temperature and 20 K is almost the same as that before forming. The elongation of the shell at room temperature increases after forming， and the elongation of the bottom of the shell at 20 K decreases but still meets the requirements.