Aiming at the structure of hybrid robot for machining,the dynamic model and optimization design method of hybrid robot were proposed. The dynamic model of the hybrid robot was established,and the three performance indexes of the robot workspace/machine volume ratio,lateral stiffness and low-order mode were comprehensively considered. The influence of design variables on the performance indexes was analyzed. On this basis,the design problem and comprehensive design strategy of the internal parallel mechanism of the robot were formulated,and the structure of the robot was optimized. A multi-DOF hybrid robot experimental platform was buit.The test results show that the designed hybrid robot has good static and dynamic characteristics in a large workspace,and the rationality of the proposed model is verified.