In this paper, an impedance composite control based on disturbance observer is proposed for manipulator system with unknown disturbances. For tracking the desired second order impedance dynamic model, the composite control strategy is designed, which includes disturbance observer (DOB), the impedance controller and the position controller. First, disturbance observer is used to estimate the unknown disturbances; then impedance controller corrects input angle; then position controller tracks the adjusted angle; finally, this composite control strategy ensures the impedance error can converge to a small neighborhood. The desired dynamic tracking of the second order impedance model is realized. The effectiveness of the proposed control method is proved by simulation examples.