Abstract: Based on the theory of the thermos-gas-lubrication, an analytical mixed lubrication model for the high-temperature gas hydrostatic seal is established. The influence of the temperature and the surface roughness factors on the gas leakage rate is numerically analyzed. It is shown that the influence of the temperature on the leakage is significant in view of the viscosity effect and the rarefaction effect. The higher the temperature, the lower the leakage will be. When the temperature increases from 200 K to 400 K, the leak rate can be reduced by more than 20%. Besides, the leakage rate is also affected by the surface roughness in value, orientation and distribution pattern. The surface roughness value is the main factor affecting the leak rate of the gas static seal. The lower the roughness is, the smaller the leak rate will be. When the surface roughness R _a decreases from 0.8 mm to 0.1 mm, the leakage rate can be reduced by about 3 orders of magnitude. The engineering realization of the low leakage rate static sealing surface depends on the reasonable design and machining for the surface roughness.