Deep hot dry rock (HDR) geothermal energy is a widespread and sustainable renewable energy that could be extracted for the decarbonisation of electricity generation. Measurements are essential for hydraulic fracturing in HDR monitoring, which can be used for assessing the current state and predicting the future performance of geothermal systems. However, a major challenge is that it is difficult to implement hydraulic fracturing for HDR under high-temperature and high-pressure (HTHP) conditions. Similarly, it is hard to conduct laboratory-scale hydraulic fracturing experiments under HTHP due to the sealing failure of injection pipes in boreholes. Therefore, in this paper, we proposed a novel sealing technique by using a wedge-shaped structure for sealing injection pipes under HTHP environments. By conducting numerical simulations and experimental verifications, we discovered that (1) compression stress should be applied on the seal to achieve pre-sealing. Specifically, a compression displacement of between 2 mm and 6 mm is suggested. (2) Copper material with good ductility, high-temperature bearing performance, and excellent thermal expansion is preferred for manufacturing the seal components. (3) Heating-induced thermal expansion of sealing is conducive to re-sealing rocks.