In order to provide data on diffusion coefficients and solubility constants of tritium in molten salts for the critical issue of tritium control in the Thorium Molten Salt Reactor (TMSR) program, a two-chamber permeability apparatus separated by a nickel plate had been developed for determining the permeability of hydrogen isotope in molten salts. Descriptions on the permeability apparatus, experimental procedure and the analytical method for determining the diffusivity and solubility of hydrogen isotope in molten salts were presented in this paper. To assess the performance of the apparatus, the blank tests without molten salt were conducted at 300–700 ℃. The results showed that the nickel plate acting as the window for hydrogen isotope permeation in the apparatus seemed to have less effect on experiments of determining the permeability of hydrogen isotope in molten slat at 500–700 ℃. Furthermore, the applicability of the apparatus with molten salt was also evaluated experimentally, with test experiments of molten Flinak (LiF-NaF-KF) at 500 ℃, 600 ℃ and 700 ℃. Diffusion coefficients and solubility constants of hydrogen in molten Flinak can be derived from those test experiments, which were correlated to,$D_{\text{Flinak}-\text{H}}={7.06\times 10}^{-5}{e}^{-54.9/(R_{\text{g}}T)}$,m,2,/s and,$S_{\text{Flinak}-\text{H}}=1.67\times {10}^{-7}{e}^{27.0/(R_{\text{g}}T)}$,mol-H,2,/(m,3, Pa).