Aiming at the problem of dynamic obstacle avoidance in complex scenes such as floating objects and space debris dense areas, a three-dimensional A* optimization obstacle avoidance algorithm for dynamic obstacles is proposed, which is mainly used to complete the path planning tasks of spacecraft and small space robots in the above environment. This algorithm extends the traditional two-dimensional A* algorithm to three-dimensional, and then optimizes the path through fuzzy judgment rules to realize the real-time optimization of the motion path and reduce the energy consumption in the three-dimensional gravity free environment. Simulation results show that the algorithm can effectively avoid obstacles in three-dimensional environment, and the optimization index is nearly doubled, and the energy consumption is effectively reduced.