An adaptive variable impedance control for force tracking is proposed, which has the capability to track a specified desired force and to compensate for uncertainties in environment location and stiffness. Firstly, by establishing the interaction model between robots and environment, the requirement of environment stiffness and location are analyzed. Then, a new impedance model is developed to adapt any uncertainly environment stiffness. According to the change of contact force, the impedance parameters can be adaptively adjusted on-line to compensate the unknown dynamic environment. And the stability of the adaptive variable impedance control is proven. Finally, the classical constant impedance and the adaptive variable impedance proposed are compared in the unstructured environment. The experimental results show that the proposed scheme can achieve better force tracking performance than the constant impedance control.