Hot dry rock （HDR） is a clean and renewable energy resource developed mainly through enhanced geothermal systems （EGS）. In EGS engineering， geothermal drilling technology is required for the construction of both injection wells and production wells， and the formation fracture and wellbore collapse during high temperature and high pressure drilling are important problems in hot dry rock drilling construction. Under the action of temperature difference， the temperature stress is generated between mineral particles due to the difference of thermal expansion and cold shrinkage characteristics of mineral particles of rock， which results in thermal fracture of rock mass. In this paper， with the help of RFPA numerical simulation software， the fracture propagation of granite in wellbore under the action of cold shock during hot dry rock mining is studied. The results show that during the cold shock process of the wellbore model， as the increase of the cold shock time， the tensile stress on the rock surface first increases to a peak value and then decreases slowly. The fracture growth can be roughly divided into early， middle and late stages. In the early stage， an annular tensile stress zone appears around the wellbore and uniform micro-cracks begin to appear. In the middle stage， with the increase of time， the tensile stress zone gradually spreads to the periphery of the wellbore and the fracture spreads outward beyond the tensile stress zone. In the late stage， the tensile stress gradually decreases to less than the tensile strength of the model， and the fracture propagation slows down until it stops. The confining pressure， well diameter and temperature have a significant impact on the damage effect of the surrounding rock under cold shock. Among them， the temperature and well diameter promotes the growth of cold shock fracture while the confining pressure inhibits it.