In hydrogen stations for fuel cell vehicles, a rapid filling process of high pressure hydrogen to a tank on the vehicle is requested, and there are some concerns that possible condensation of residual water at a low temperature section in the fuelling system leads to occlusion in pipes or instability of flow system. In the present investigation, dew and frost point measurement system for residual water in high pressure hydrogen utilizing cooled mirror technique with original image analysis had been designed and developed. Frost point measurements with hydrogen-water standard gases under conditions of 5〜10 MPa, 5〜55 ppm were carried out systematically, and frost point estimation procedure was also developed utilizing new frost point data.