【Purposes】 Coal mine underground terrain is complex and changeable and the air contains a variety of inflammable and explosive gases, which has high risk. In order to reduce the risk and improve the efficiency of inspection, a separable wheelleg quadruped robot with multiple motion modes is proposed in this paper. 【Methods】 Five main motion modes of the robot, including leg mode, wheel mode, wheel leg mixed mode, body separation combined mode, and arms clamping mode were analyzed. The single leg structure parameters were described and the leg working space of the robot was drawn on the basis of Monte Carlo method. The acceleration reversal method was used to eliminate the abrupt change of foot longitudinal acceleration, and the foot trajectory under the leg mode was optimized. According to the trajectory characteristics of quintic polynomial, the wheel leg switching trajectory of multiple motion modes was planned. On the basis of the joint simulation environment of Webots and MATLAB, the stability of Trot gait and the flexibility of wheel-leg mode switching track under the robot leg mode were verified. 【Conclusion】 The research content of this paper provides a theoretical basis for the separable wheelleg quadruped robot that can carry out inspection in mine environment.