Abstract: A wheel-legged robot is proposed, which is comprised of the front wheel-leg module, the rear wheel-leg module, and the active waist joint. The research indicates that the locomotion of the wheel-legged robot with the rigid waist joint in trot gait is unstable with violent vibration. According to the biological study in quadrupeds and ZMP (zero moment point) based real-time trajectory planning with sway compensation, a control method using the active waist joint is proposed to improve the locomotion stability in intermittent trot gait. Kinematic and dynamic models of the wheel-legged robot are developed. Experimental results show that the addition of the regular swinging function for the yaw joint can dramatically reduce the amplitude of the body vibration from 62.2 mm to 12.8 mm and remarkably improve the locomotion stability of the robot in intermittent trot gait.