The exploitation of shale oil resources is significantly influenced by the connectivity of reservoir fractures. The formation of a complex fracture network is challenging due to the fact that shale reservoirs have an extremely low permeability and lack the development of natural fractures. Consequently, the issue is typically resolved by injecting into the rock to create artificial fractures, thereby enhancing the permeability of the formation. The micro-pores and micro-cracks evolution of shale reservoirs after high temperature convection heat exhibit significant differences, and the shale fracturing caused by high temperature is also evidently distinct in its mechanism. In addition to altering the mechanical mechanism of rock fracture, it also has a significant impact on the fracture morphology of shale reservoirs. The formation of fractures by high-temperature thermal fluid is an exceptional method for enhancing production. This method can create a large-scale fracture network in underground rock strata and enhance production efficiency. At this juncture, the most economical and effective research method for resolving numerous geological engineering issues is numerical simulation analysis of multiphysics coupling in porous media. In this investigation, numerical simulations of shale fracture propagation during high-temperature thermal fluid injection were conducted using the established thermo-hydro-mechanical coupling shale model. The research results indicate that the shale fracture propagation is the result of the combined action of hydraulic action and thermal stress under the influence of high-temperature convection heat. The most significant factor in fracturing is thermal stress. The primary fracture commences at the wellbore and advances in the direction of the maximal principal stress. The fracture propagation behaviour becomes more complex, the fracture initiation pressure decreases, and the rock mechanical properties diminish.