The model of the mechanical arm for demolition was established,and the dangerous working condition of the robot arm was determined,and statics analysis was conducted for this condition. According to the analysis results,the machine arm was topologically optimized with the aim of light weight. Based on the results of topology optimization,combining with actual manufacturing technology,the structure of the mechanical arm was optimized. The optimization results indicate that the mass of the mechanical arm is reduced by 31.9%.At the same time,both the intensity and rigidity of the mechanical arm meet the requirements. It provides reference for the research and development of the machine for demolishing buildings.