Abstract: Non-Fickian diffusion is one of the important phenomena often observed in chemical processes, especially in polymer-related diffusion, and of which “overshoot” is interesting.The Jou model based on the EIT theory was used to study “overshoot” behavior observed in polymer diffusive system.After simplification of the Jou model,a diffusion dynamic equation, which was characterized with hyperbolic type, was obtained, then simulative analysis for three combined dimensionless parameters was done to research various diffusion behavior resulted from the change of model parameters.Results indicated that, the equation could describe “overshoot” phenomenon, so that the cause of “overshoot” could be interpreted theoretically/mathematically.The existence of the intrinsic relaxation time for diffusion was a necessary requirement, and with appropriate existence of diffusive retardance, that diffusion time greater than relaxation time was a sufficient requirement for “overshoot” behavior.