Mobile robot motion planning is one of core technologies in mobile robot navigation. According to the contradiction between the intelligence and the control precision of mobile robot as well as the behavior fusionspsila insufficiency in traditional motion planning method, a layered motion planning method is presented. Behavior is arranged in different layer according to its objectpsilas relation, lower behavior takes upper behaviorpsilas output as its references, the lowest behavior output the finally fusion results. Finally, taking robot motion planning in unknown dynamic environment as research background, the layered motion planning architecture is realized. The validity of the method is proved by simulation experiment.