Drilling-hole trajectory measurement is an indispensable technology of the exploration and development of HDR. However, this technology at present stage cannot meet the requirements of inclination measurement in HDR strata. High temperature and high pressure at the hole bottom is the key problem. For this reason, by the double-layer outer tube structure design with the pressure-bearing probe tube and non magnetic thermos bottle, the use of the advanced hard magnetic calibration, the selection of high temperature resistance elements and low-power circuit design, GRY-1 inclinometer is developed to meet the requirements of the drilling-hole in HDR strata at the temperature up to 280℃ and depth of 3000 meters. The practical results show that GRY-1 inclinometer has good applicability in HDR strata and can contribute to the exploration and development of HDR resources.