Abstract: The multi-source factors such as the weight of the beam and the weight of other functional components together cause the Z-direction depression and torsional deformation of the beam guideway Surface,it will leads to the distortion of the accuracy of the guideway surface and affects the Y-direction comprehensive straightness of the beam of the gantry machining center. In order to eliminate the influence of unfavorable factors on the surface of the guide rail, based on the finite element analysis method, this novel focuses on the upper and lower guideway Surfaces of the beam.Then the simulation analysis test scheme was established and the deformation at different positions were solved. According to the whole deformation curve drawn by the fitting, the deformation of the guide rail Surface was repaired and compensated. The actual measurement results show that: The Y -direction comprehensive straightness accuracy of the crossbeam of the gantry machining center is effectively improved after compensation.