Specifying of the dynamic behavior and impedance characteristics determination of the patients’ lower limb is a necessity for interactions with rehabilitation set-up. In simple proposed models of previous researches, the effects of joint angles on the impedance properties of the leg were not considered and the parameters were identified by nonparametric methods. Hence, the results of identification were not so much appropriate to analyze the rehabilitation process. So, in this paper, a 3 DOF nonlinear dynamic model is developed regarding to the angular stiffness and damping of the lower limb joints and moment of inertia of its moving organs. Then, a linear model is presented to identify the parameters by PEM method. The linearization and identification precisions are evaluated individually. The leg’s parameters are identified for 3 subjects with different mass numbers at four distinctive configurations which are considered during the walking. The identification accuracy is evaluated by comparison between the identified and geometrically estimated mass moment of inertia. Ultimately, the interaction performance of the patients’ leg with rehabilitation pneumatic actuator is investigated considering to leg rigidity and the amount of overweight. The results demonstrate good accuracy and high performance of the linear model for parameters identification.