Aiming at the problems of RRT* algorithm in path planning in complex obstacle environment, such as blind search, redundant nodes, unsmooth path and easy approach to obstacles, a Magnified Obstacle-based Bidirectional Dynamic Goal Bias RRT* (MOBDB-RRT*) algorithm is proposed.Firstly, the obstacles are magnified to ensure a safe running distance for the robot.Then, based on RRT* algorithm, a bidirectional dynamic goal bias strategy is introduced, which reduces the time of searching the path and improves the planning efficiency of the algorithm.Finally, pruning algorithm and cubic Bézier curve are used to optimize the planned path, so as to generate a shorter and smoother path.The simulation results show that the improved RRT* algorithm is superior in path planning efficiency and path quality.