The invention discloses a mechanical arm motion planning method for improving a bidirectional RRT algorithm. The method integrates the traditional bidirectional RRT algorithm, an optimal searching mode of a parent node is introduced and a connecting mode of a node is updated, the distance of the mechanical arm path planning is greatly reduced, the searching speed of the bidirectional RRT algorithmcan be guaranteed and an optimal path is planned; and the target position of a mechanical arm is given and the obstacle information in the environment is acquired, a collision-free path is planned byadopting an improved bidirectional RRT algorithm, and the mechanical arm moves to the target position according to the planned path, so that the motion planning of the mechanical arm on the basis ofthe improved bidirectional RRT algorithm is completed. According to the mechanical arm motion planning method for improving the bidirectional RRT algorithm, the improved bidirectional RRT algorithm isadopted, so that the planning path cost can be greatly reduced, the optimal path is planned for the mechanical arm, and the problem that the motion path is not optimal is solved; and the method not only is suitable for motion planning research of mechanical arms in a high-dimensional space, but also can be applied to the field of mobile robots, and has a wide application prospect.