In recent years, CCS (CO₂ Capture and Storage) , which capture CO₂ from CO₂ emission source and storage it in ocean, for mitigation of global warming has been expected. Especially, the method using depression region in seabed that can be stored huge amount of CO₂ and reduce the influence on surrounding environment is required to practical use. In this method, CO₂ hydrate is formed at the interface of liquid CO₂ and seawater like a film form. It is required to clarify the molecular diffusion in the CO₂ hydrate and the mass transfer behavior of CO₂ through the hydrate film into water. In this paper, we focused on CO₂ transport behavior from interface between the hydrate and water to dissolution water and aimed to estimate mass transfer coefficient and diffusion coefficient in dissolution water under hydrate formed condition. We visualized CO₂ dissolution behavior to water and changing of pH distribution in timeseries using a pH indicator in a pressure resistance visualization apparatus under hydrate formable conditions. We performed image processing to visualized images and estimate those coefficients. As a result, CO₂ mass transfer was influenced by concentration state of dissolution water and visualized diffusion behavior was like a behavior with large diffusion coefficient.