In order to solve the process problem of over-deformation caused by the release and redistribution of residual stress in the material removal process of large thin-walled casting guideway beam, the processing technology of guide beam parts was analyzed to realize the simplification of part model and substructure segmentation. At the same time, the surface residual stress measurement of the part blank was carried out, and the initial stress model of the part blank was successfully established. On this basis, the finite element simulation of part machining is carried out in combination with the actual machining process. The residual stress release caused by material removal during machining is simulated, and the residual stress redistribution law and machining deformation during machining are predicted. Summarize the finite element simulation results of the machining deformation of the parts, and propose a process plan to suppress the machining deformation of the parts. It is verified that the improved process sequence reduces the maximum deformation of the parts from 0.485 mm to 0.081 mm, which is reduced by 83.3%, and avoids the oversize of the parts during processing. At the same time, this plane is used as the benchmark for subsequent processing, which ensures the accuracy of subsequent processing and provides an effective theoretical basis for the optimization of production process.