Abstract: One of the difficulties of the control problem of the robot force control system is that the stability of the system is sensitive to the changes of the stiffness of the environment on which the force is exerted. To solve the problem, this paper first presents a model of the manipulator in contact with a rigid environment and then proposes an adaptive force control method based on the Popov’s hyperstability criterion. The principle of the method is to identify the environment stiffness to determine an adaptive force feedback gain corresponding to the contacted environment.The theoretic analysis and experimental results show that this method can realize a stable force control when the environment stiffness changes in sufficiently large extent.