The invention discloses a high-temperature high-pressure hydrogen diffusion testing device which comprises a high-temperature autoclave, wherein a sealing sleeve is arranged on the side wall of the high-temperature autoclave along a radial direction; one end of the sealing sleeve is positioned in a reaction chamber of the high-temperature autoclave, and the other end of the sealing sleeve convexlystretches out of the outer side wall of the high-temperature autoclave; a sample holder is embedded into the sealing sleeve; the sample holder is in sealed connection with the outer side wall of thehigh-temperature autoclave; the inner side end of the sample holder is communicated with the reaction chamber; the inner cavity of the sample holder is communicated with an anode hydrogen evolution reaction tank; the side face of the sample holder is connected with the high-temperature autoclave in a hard sealing manner; an insulating device and a polytetrafluoroethylene pressure ring are arrangedat the front end of the sample holder; the sample is arranged between the polytetrafluoroethylene pressure ring and the insulating device; a wire connected with the sample passes through the insulating device and is led out of the sample holder to be connected with an electrochemical workstation; a reference electrode and an auxiliary electrode are arranged on side walls of the anode hydrogen evolution reaction tank; the reference electrode and the auxiliary electrode are connected with the electrochemical workstation. The high-temperature high-pressure hydrogen diffusion testing device has the characteristics of being simple in structure, convenient in installation and comprehensive and no-missing in detection.