A posture control system based on the controlled contact force was designed to ensure there is no slipping between the foot of Acrobot(acrobatic single-leg robot) and the ground during motion. The horizontal component of the contact force was set as the control objective of the internal loop and its value was restricted by the friction cone, so that the contact consistency between foot and ground at the tracking process of the shank′s posture angle was preserved. At the upright equilibrium posture of Acrobot, the dynamic equations were linearized and the transfer function link “actuation torquehorizontal contact force-horizontal position of the center of mass-posture angle of the shank” was derived to design the multi-loop control system for the posture angle of the shank. A virtual Acrobot model was built in MATLAB by using the “SimMechanics” toolbox. Simulation results show that the designed control system can realize the tracking control without slipping between the foot and the ground.