In order to store huge CO₂ as from a thermal power plant in deep-ocean using CO₂ hydrate, CO₂ hydrate film thickness was measured under some temperature and ambient flow velocity conditions. Once the film was formed at the interface between CO₂ and water, the film thickness was measured continuously during several hours. As a result, the film thicknesses decreased with experimental temperature and ambient flow velocity increasing. Furthermore, the film thicknesses approximately maintain its initial film thickness when hydrate film formed at the interface. Thereafter, the prediction model for CO₂ hydrate film thickness was developed based on mass transfer. As a result of comparison each measured and predicted film thickness, it is clarified that the film thickness at initial stage can be predicted using the amount of CO₂ enclosed in the CO₂ concentration distribution before hydrate formation and saturation concentration of CO₂ with CO₂ hydrate. On the other hand, growth behavior of CO₂ hydrate is predicted by considering the permeation of water molecule through hydrate film. The predicted value with time indicate good agreement with measured values.