Desorption kinetics of hydrogen isotopes implanted into type 316L stainless steel by glow discharge have been studied by the experiment and numerical calculation. The temperature of a maximum desorption rate depended on glow discharge time and heating rate. Desorption spectra observed under various experimental conditions were successfully reproduced by numerical calculation which is based on a diffusion-limited process. It is suggested, therefore, that desorption rate of a hydrogen isotope implanted into the stainless steel is limited by a diffusion process of hydrogen isotope atoms in bulk. Furthermore, small isotope effects were observed for the diffusion process of hydrogen isotope atoms.