The invention relates to an improved dynamic RRT* mobile robot motion planning method. According to the method, all collision detection in an original RRT* algorithm is eliminated, and a cost functionvalue is controlled by adding a collision risk assessment component in a cost function. When a sampling point or edge collides with an obstacle, the component is remarkably increased, the cost function value is promoted to be synchronously and remarkably increased, the possibility that the point and the edge colliding with each other continue to expand is restrained, and therefore, the algorithmhas the obstacle avoidance capacity. Because the method has no collision detection, compared with an RRT* algorithm, the convergence speed is higher, the efficiency is higher, and the advantages are more prominent in the more complex environment in the aspect of the movement planning problem of the mobile robot.