Abstract： Based on the flexible body movement principle of quadruped creatrures, a kind of bionic flexible body for quadruped robot was presented, which was composed of pneumatic artificial muscles (PAM), bionic spine,fore body and hind body. The geometric method was adopted to analyze the kinematics of the bionic flexible body, and the relationship between the body bending angle and the PAM length when the quadruped robot walks with spinning gait. The body bending can be controlled by controlling the PAM length. The dynamics of bionic flexible body was derived by the floating coordinate method and moment of momentum theory. Then the PAM driving force for body bending with different body kiffness was determined. The experimental system was conducted, and the PID control algorithm was adopted to analyze the body bending. This paper can lay a foundation for improving the mobility of the quadruped robot walking in unstructured environment.