The Well A is part of China’s pioneering hot dry rock (HDR) demonstration project. During the third section drilling, a collapse at 3519.14 m resulted in a disconnected drill pipe, with the drill bit and fishing tools remaining at the bottom. This incident necessitated the development of advanced sidetracking techniques to reach the target depth of 4000 m safely and efficiently. Based on earlier drilling operations, several difficulties in directional sidetracking within geothermal HDR formations were identified. These challenges include maintaining borehole stability, managing high temperatures, and ensuring the longevity of drilling tools. Theoretical calculations and comparative analysis were conducted to determine the optimal parameters for sidetracking. This included evaluating drilling procedures and enhancing mud cooling technologies. Experiments on high-temperature (HT) thickening and cement stone curing led to the selection of a HT-resistant cement slurry system, which is crucial for maintaining the sealing quality of the geothermal section. The high temperatures encountered significantly reduced the lifespan of drilling tools and equipment. To mitigate this, a forced mud cooling technique was implemented, lowering the outlet mud temperature from 75°C to about 57℃, thus enhancing operational efficiency and equipment durability. Data from neighboring wells were utilized to select a sidetrack initiation point at 3370 m. Using Landmark software, the wellbore trajectory was accurately calculated. The construction phase employed a drill bit with a diameter of 216 mm, combined with a 2° bent sub and a 1.5° bent motor assembly, successfully creating a new wellbore around the obstruction. The successful implementation of sidetracking in the Well A has established a robust technology system for HT hard rock, particularly in geothermal formations. This case study provides a practical reference for addressing complex drilling conditions in similar geothermal projects. The Well A sidetracking project has significantly contributed to the technological advancements in geothermal drilling. By overcoming the challenges of HT hard rock formations, it provides a critical framework and reference for future geothermal drilling endeavors.