Typical materials for components, type 316 stainless steel (316-SS), were chosen as a sample and hydrogen isotope was charged by various methods, water adsorption, electrolysis and ion irradiation to elucidate hydrogen isotope behavior on/in SS. The chemical states of SS surface were studied by XPS and the hydrogen isotope retention and its desorption behavior were analyzed by TDS. Two types of surface finish, namely non-pretreated sample and pretreated sample by polish and annealing were prepared. It was found that the oxy-hydroxide and hydroxide were formed on the surface layer. The hydrogen isotope desorption stages consisted of three stages, namely the desorption stages from oxy-hydroxide, hydroxide and bulk hydrogen. A large amount of deuterium was trapped by the oxy-hydroxide layer for the non-pretreated sample with electrolysis. The hydrogen isotope trapping by this layer would have a large influence on the hydrogen isotope retention. The surface finish would be one of the effective improvement for decreasing its retention on SS.