The seepage and heat transfer channel of enhanced geothermal system (EGS) is mainly composed of the wellbore of injection and production wells and the random fracture network reservoirs. The previous thermal–hydraulic coupling simulation studies only focused on fracture network reservoirs, but ignored the heat transfer of wellbore wall, so the simulation results are less accurate. For more accurate evaluation of the performance indexes of EGS (e.g. output and life), the thermal–hydraulic coupling of wellbore and random fracture network reservoir was numerically simulated in this paper. Then, based on the commercial finite element software COMSOL Multiphysics, the coupling solution of seepage field and temperature field of wellbore and reservoir was conducted, and the factors affecting the recovery temperature and thermal mining rate of EGS were analyzed. And the following research results were obtained. First, the opening length (L0) of injection/production wells has an important effect on the productivity and life of EGS. The optimum opening length is 400 m, and its corresponding EGS has the optimum output and life. Second, installing thermal insulation materials on the wellbore wall can effectively increase the recovery temperature at the beginning and early stage of mining, reduce the heat loss and improve the mining rate. Third, as the mining goes, obvious low temperature zones occur around the injection well and advance to the production well along the fracture channel, and consequently the system will reach the recovery life and become exhausted. In this case, the thermal energy recovery shall be continued after stopping for a period of time. Fourth, the influence of fracture permeability and thickness on the thermal mining rate is in positive correlation. The increase of parameter values will lead to the increase of thermal mining rate but the reduction of mining life. It is concluded that the heat transfer of wellbore wall is of great significance to the comprehensive evaluation on EGS output and life, and the integrity evaluation on EGS can be realized by virtue of the wellbore–geothermal reservoir coupling simulation considering wellbore wall heat transfer.