Abstract: In this paper, the finite element method was used to analyze the deformation law and influence factors of the outlet flow channel caused by welding the impeller of a large centrifugal compressor. The research results showed that the deformation of the outlet runner after welding and heat treatment of impeller was mainly caused by the deformation of the cover disc, and the final deformation of the outlet height of the runner was about 2. 3 mm. After welding, the outlet height of the runner was deformed too much, so a limit block was designed to optimize the outlet runner deformation. Through the numerical simulation analysis of different positions of the limit block, the results showed that the welding deformation of the outlet runner height was reduced to about 50% after the limit block was added on the obtuse angle side of the blade,and the overall deformation amplitude of the impeller decreased.