The objective of the present study is to predict the time transition of CO_2 hydrate film thickness by the analysis. The model is developed based on the mass transport mechanism. The model is based on the hydrate formation and dissolution behavior. In the present model, hydrate formation occurs at the interface between liquid CO_2 and hydrate due to the penetration of H_2O molecules through the CO_2 hydrate film. Meanwhile hydrate dissolution occurs at the interface between water and hydrate due to the diffusion of CO_2 molecules to the water phase. The estimated diffusion coefficient of H_2O molecules as 3.1×10^<-12> m^2/s is used to the model calculation. The results indicate that the film thickness decreases within several minutes, then increases.