Micro industrial robots are widely used in various industries due to their strong coupling, scalability and high precision. However, most robots are mainly connected in series, and the problem of low structural stiffness will cause vibration in the robot’ s motion and affect the overall stability. Taking the service robot as the research object, in order to ensure the stiffness of the robot structure and the stability of the grasping process, the overall stiffness of the robot was optimized. The kinematic static model of the robot was established, and the stiffness equivalence principle was used to calculate the joint stiffness of the robot; under the constraints of the grasping posture range, the robot end stiffness ellipsoid half-axis length was used as the optimization index, the improved particle swarm optimization (IPSO) algorithm was used to optimize the stiffness of the robot at different grasping poses，and the results were compared with those of genetic algorithm and particle swarm optimization algorithm; the end deformations before and after optimization were compared through ANSYS finite element analysis and experiments. The results show that the research on the stiffness optimization of the robot gripping system based on IPSO algorithm has certain significance to improve the overall stability of the robot.