Abstract: Collision-free grasping actions of virtual human are difficult to plan especially when the surrounding scene is complex.Firstly,the forward and backward reaching inverse kinematics(FABRIK) algorithm is improved and an obstacle-avoiding FABRIK algorithm is put forward to design a collision-free grasping posture.Then,the bidirectional rapidly-exploring random tree(Bi-RRT) algorithm is adopted to plan the motion of human arm from a given initial posture to the grasping posture,which is composed of a series of intermediate postures.In addition,some strategies are developed to handle the issues of the bound constraints on the arm's 7angular parameters and the simplification to the zigzag paths generated with the Bi-RRT algorithm.This paper provides some results of computation experiments from the implementation of the proposed method,which show that the method can be used for the arm motion design of virtual human in the scene with obstacles.