Collision avoidance is quite an important issue for manipulator control, due to the safety reason for manipulator and the environment. However, most of the research concentrate on immobile obstacles in a static environment, and few studies concerns collision avoidance in a dynamic environment. In this paper, we propose a Weighted Least Norm method to avoid the collision with a moving obstacle for redundant manipulator. Simulation on a 7-DOF plannar manipulator demonstrates the validity of the algorithm.