Abstract: Robots moving in orbit to assemble space structures is one of the most promising ways to build large spacecraft, but there are serious dynamical coupling effects between the two when robots work on the structure surface, which brings new challenges to the construction of space structures. A robot-structure coupled dynamics modeling and gait optimization method is proposed for the coupled dynamics problem formed by a three-branch robot walking on a flexible structure in space. First, a robot-structure coupled dynamics model is established based on the Lagrangian equation and the Euler-Bernoulli beam model, which can be used to predict the coupled dynamics response of the robot when walking on the surface of the structure. Then, the relationship between robot motion and structural vibration is derived based on the coupled dynamics equations, and the optimization study of robot walking gait is carried out with the goal of reducing the structural vibration response. Finally, the numerical simulation of the dynamic response of the spatial structure under different creeping gait movement modes of the robot is carried out, focusing on the analysis of the influence law of the robot on the dynamic response of the spatial structure when walking with different step frequencies, different step lengths and different lifting heights. The simulation results show that the dynamic response of the spatial structure is closely related to the movement mode of the robot. Therefore, when designing the gait frequency of a walking mobile assembly robot, it should be avoided to be twice the natural frequency of the space structure. At the same time, the movement step length and lifting height should be reduced as much as possible under the premise of ensuring the safety and stability of the robot assembly. Moreover, the vibration of the space structure can be effectively suppressed by optimizing and adjusting the gait of the robot.