It was the multi unit combined spring and damp model that was widely used to study rheological properties of wood material, but its some constant coefficients were not easily solved. In this paper, a concept of variation coefficient rheological model was put forward, which adopted two unit Maxwell body of variation coefficients to simulate the creep behavior of medium density fiberboard （MDF）. Results showed that the model could be effectively used to fit the creep of the MDF, and easily to seek the rheological coefficients because of its fewer units of combination modulus of spring damper. The author also indicated that the model could fit the creep of MDF on changing load with Boltzmann superposition principle.