Abstract: Proposes a novel algorithm to determine the reference trajectory, which is to be applied to the traditional impedance model. A reference scaling factor is thus developed to tune the reference trajectory in order to adapt the reference trajectory generated for the changeable unknown stiffness in environment. The reference scaling factor is determined by fuzzy reasoning in accordance to the information feedback on forces in contact. Moreover, the impedance model parameters are adjusted fuzzily according to the change of forces in contact to reduce their disturbance in constrained motion as possible so as to improve entirely the effect of force control. The simulation results show that the proposed scheme has better force tracking performance and robustness to unknown parameters of the environment in comparison with the traditional force control method.