Abstract: In order to investigate welding stress distribution and deformation of master cylinder on 80 000 tons of die forging press, the master cylinder welding simulation model were built using finite element method, and the results of the master cylinder temperature field, stress and deformation were obtained. The results show that the maximum temperature of master cylinder is about 2 100 ℃, appearing in the weld area, and the maximum temperature gradient occurs in the joint area during the welding process. After the welding, the maximum displacement of the master cylinder is about 8 mm, located on top of the master cylinder, and the displacement amount of the weld zone is smaller compared to top of the master cylinder. In order to prevent large deformation and ensure assembly accuracy after welding, the displacement at top and bottom of the master cylinder must be constrained before welding. The maximum stress of master cylinder is about 470 MPa, appearing in the weld area, the stress in heat-affected zone is lower, which followed by the base metal zone. Before the heat treatment, it should be checked whether there are cracks on the surface of welding or other welding defects. These results can provide calculated data reference for actual production of the master cylinder.