Taking the big arm of ER20C10 six degree-of-freedom industrial robot as the research object, in view of its light weight, high strength and good dynamic characteristics, the statics analysis of the big arm was carried out by using solidThingking Inspire software, and the modal analysis of the large arm was carried out by using ANSYS Workbench software to determine whether the big arm model was reasonable or not and to provide basis for the final effect verification. The topology of the large arm was optimized by using solidThingking Inspire software, and geometric cleaning and meshing of the optimized arm were carried out by using ANSA software. Finally, the modal analysis and statics analysis of the optimized arm were carried out. By comparing the analysis results before and after optimization, it is found that the optimized arm not only has improved strength, stiffness and minimum safety factor, but also realizes lightweight.It provides reference for the research and development of industrial robot mechanical structure.