Abstract: Using the long span and heavy load crossbeam of some machine tools plant's heavy-type numerical control milling planer as a subject,this paper builds a model and force analysis through the finite element software.The force distribution and deformation condition of the long span motion girder under the actual working condition are also studied.The describing method and establishing process of the long span load curve,which considers the strolling board superposition effect,are built by contacting analysis and restraining analysis.The tool tip's trajectory deformation is obtained.The research provides a sufficient theory basis and simulation method for improving the crossbeam structure and obtaining a perfect arch in advance.