Conductivity in hydraulic fractures embedded with proppants has a great impact on the efficiency of geothermal development in an enhanced geothermal system. This study explores the effects of proppants and hydraulic fracture arrangement on the efficiency of geothermal development by developing a thermo-hydro-mechanical coupled model. The evolution of the fracture aperture is captured based on the Hertz contact theory and the Kozeny-Carman equation. The finite element method (FEM) is used to analyse the mechanical behaviour of the fractured system. The thermo-hydro circulated process is investigated using the unified pipe-network method (UPM). In the simulation of a doublet system embedded with propped hydraulic fractures, the increase of proppant distribution density enhances the net heat-extraction rate and reduces the thermal breakthrough time and accumulated thermal energy. The influence of reservoir properties on the heat production is further investigated. In the designing of the hydraulic stimulation, both the increase of the propped hydraulic fracture number (at least two hydraulic fractures) and the spacing promote the efficiency of geothermal development, however, the cost of the field design should be considered for optimization.