Aiming at the physical coupling feature between the finger and the hand exoskeleton, a human-robot interaction modeling approach is proposed. The muscle motion formulas are established based on the finger physiological structure and Hill model. The equilibrium equations between exoskeleton and finger are connected by static analysis. In order to solve the redundancy problem of the system, a method based on the physiological cross-sectional area (PCSA) is adopted to get the optimized solution of muscle force, and an optimization method based on the total minimum error (TME) is presented to obtain the parameters of Hill model. The experimental setup is established to receive the finger data of motion and force for optimization. The approach proposed can get the quantifiable muscle parameters to study the statistical analysis of muscle motion and rehabilitation state. And it will be possible for the exoskeleton and the finger to be combined as a controlled plant so as to introduce muscle parameters into the controller design.