Research has been conducted on a piston type positive displacement pump, which is a system for the direct pressurization of hydrogen, used as a filling technology in the automobile hydrogen stations for the delivery of pressurized hydrogen gas to fuel cell powered vehicles. Development of the material for the piston ring of the high pressure liquid hydrogen pump had been investigated in order to improve the life time of the piston ring. One of the candidates for the ring material were PTFE (Polytetrafluoroethylene) and PEEK (polyetheretherketone). But we suggest other new material and seal material life assessment experiment had been conducted in liquid nitrogen and liquid hydrogen. Improvement of the seal material life time for the piston ring of the high pressure liquid hydrogen pump was confirmed in the life assessment experiment in liquid hydrogen.