A long-term, reliable high pressure reference electrode for high temperature applications was disclosed. This reference electrode has inner and an outer liquid junction plugs. The inner plug provides the function of restraining the outflow of the internal reference electrolyte. The outer plug is chemically and mechanically robust in the external fluid where the reference electrode is used and protects the inner plug from the mechanical and chemical attacks by the harsh external fluid. Therefore, the inner plug can be selected from many of the well-characterized liquid junction plugs used in regular low temperature reference electrodes, without the need for the inner plug to be chemically and mechanically stable in the external fluid, as long as it has the thermal stability.A method for preventing the formation of gas bubbles inside a high pressure reference electrode in the electrolyte-filled section, and thus eliminating the gas bobble effect on the electrical continuity, was also disclosed. One or more thin solid rods or tubes are inserted into the internal electrolyte-housing tube and the thin rods or tubes alter the surface tension of the gas bubbles so that the bubbles are unstable in the middle of the liquid electrolyte. Compared with the fiber wicks or porous powder used by previous researchers to ensure the electrical continuity, the thin tubes or rods are easier to handle and easier to clean. This method may also be used in other systems that contain a liquid-filled tube (e.g., a pH electrode) to prevent the formation of gas bubbles in the liquid-filled section of the tube.