As the main executive mechanism of the robot’〖KG-*2〗s grasping task, the rational structure design and terminal reachable space of mechanical arm are always the research hotspots. The forward kinematics model of the mechanical arm was created by using the improved D-H method according to the configuration characteristics of the mechanical arm, and the accuracy of the model was verified by comparing the numerical calculation and simulation results. The working space of the end robot hand was analyzed by using Monte Carlo method, and the working points cloud map and working boundary of the end robot hand were obtained. The convhull function was used to deal with the boundary point cloud, and the envelope space was generated to solve the workspace volume. On this basis, the influence law of the structure parameters of the mechanical arm on the workspace volume was further analyzed. It provides reference for the optimization of the structure parameters, motion control and trajectory planning of the mechanical arm.