Abstract: To solve the problem that manipulator may collide with the obstacles during the run-time in its work space, two technical measures are proposed in this paper: cylinder enveloping collision detection method and variable-step segment-searching method based on A<sup<*</sup< algorithm. Using former method, the problem of collision detecting can be transformed to detect the positions between two cylinders; while the problem of using traditional A<sup<*</sup< algorithm in path searching that lead to large searching data even infinite loop searching could be solved by using the variable-step segment-searching method. The effectiveness and feasibility of proposed methods are proved by simulation on three-dimension platform based on OpenGL and application to actual system.