Abstract: In order to study the hydraulic fracture initiation and propagation mechanisms in deep hot dry rock (HDR) reservoirs, a fluid-solid-heat coupling numerical model for fracture propagation simulation was established based on the phase-field method. This model was used to analyze the mechanical behavior of hydraulic fracture propagation in HDR reservoirs, as well as the effects of factors such as temperature, pump rate, and natural fractures on the hydraulic fracture propagation. The results show that this fluid-solid-heat coupling numerical model has a relatively simple criterion with high calculation accuracy. During the process of hydraulic fracturing in HDR reservoirs, thermal stress acts as tensile stress, which contributes to increasing fracture aperture and facilitating fracture propagation. The larger temperature difference between fracturing fluid and formation, and the higher pumping rates, the more significant effect of the thermal stress. After encountering natural fractures, hydraulic fractures will communicate and initiate those natural fractures, and the re-initiation of fractures is controlled by in-situ stress and natural fractures. The findings of this study can provide a good reference for guiding hydraulic fracturing in deep HDR reservoirs.