Abstract: Conflict will take place between the trajectory tracking motion and the obstacle avoiding motion of the end-effector of the redundant robot, if the motion of the end-effector is disturbed by any obstacles in the obstacle avoidance problem of redundant robots. To deal with the obstacle avoidance problem, an obstacle avoidance algorithm based on transitioning between the primary and the secondary tasks is presented. Firstly, the obstacle avoiding motion is defined in one dimensional operational space, and two transitioning variables are used to make a smooth, continuous priority transition between the trajectory tracking motion and the obstacle avoiding motion of the end-effector using the real-time minimum distance. Finally, the validity of the algorithm is manifested by simulation of a 3-DoF plane robot. Results show that the closest distance between the manipulator and the obstacle is greater than 0.02m, while the end-effector of the robot can get the target position accurately. As a conclusion, the redundant robot can not only realize the obstacle avoidance, but also prevents the conflict between tasks by the proposed approach.