As ascending and descending stairs are typical and common actions of human, it is essential to study the algorithm of action generation of walking stairs so that steady gait can be solidly performed. Taking biped robot as research object, and descending stairs motion as example, an action generation approach based on upper body gravity move method under the principle of repeatedly direct kinematics(RDK), is proposed. Through simulating three typical modes of descending stairs, variations of angle and torques at each joint and the stability of this approach are evaluated. Also the impact of stair parameters on load of robot’s joints is discussed. The simulation shows that changing the modes of descending stairs can reduce load on injured leg joints, improve safety, and achieve stable action of descending stairs. The result provides a basis for health care and medical education.