Abstract: A novel quadruped robot with variable structure was analyzed by kinematic methods. First, the velocity of a single leg was studied. Then the kinematics of the whole robot was discussed, and a globe velocity equation was proposed and established with considering the transformation and motion of the robot's body and four legs. At last, the method of velocity decomposition control, which is usually used in the serial-chain manipulator control, was generalized to the legged mobile robot (serial and parallel hybrid mechanism) control through applying the globe velocity equation. The contraction of the robot's body with four feet fixed on the ground was taken as an example to demonstrate the feasibility of this approach.