In view of the drawbacks of expensive time cost and insufficient obstacle avoidance, a novel approach for motion planning of mobile manipulator is proposed from the perspective of mobile manipulator and series arm, which solves the obstacle-avoidance-region through self-motion analysis and obstacle classification. The geometrical characteristics of environment model, obstacle and manipulator's axis are deeply analyzed, and then the criterion for obstacle avoidance is established with the self-motion characteristic of mobile manipulator. Furthermore, the obstacle-avoidance-region is solved according to the obtained criterion, and the motion planning can be accomplished in the light of obstacle-avoidance-region. By this approach, the spatial obstacle avoidance problem can be transformed into the superposition of a plane analytical problem and a one dimensional search problem. Although this approach is not purely an analytical solution, it greatly decreases the computing complexity and ensures the sufficiency for obstacle avoidance compared to the traditional numerical method. The practicability of this method is verified by the given experimental results. © 2010 Journal of Mechanical Engineering.