A composite element model is developed for the coupled seepage-heat transfer of fractured rock mass based on the composite element method (CEM). The proposed model has simple and convenient preprocessing function, an unrestricted mesh generating system, and the automatic simulation of fractures in term of their real information in the elements. In addition, the iterative algorithm is employed to perform the coupling analysis of seepage field and temperature field. The influence of thermal on the dynamic viscosity of fluid is considered, and the fluid flow, heat transfer, flow and heat exchange between fractures and the neighboring rock blocks can also be calculated by the iterative algorithm. Moreover, the proposed method is validated by approximately analytical solutions. Numerical examples show that both fluid flow and heat transfer are influenced by the coupling effect of seepage and thermal fields. It is also found that the thermal conductivity coefficients of different rock blocks and fracture aperture affect the effectiveness of heat extraction significantly, and even have direct impact on the outflow temperature. The results demonstrate that the greater fracture aperture is caused by the higher thermal conductivity. Furthermore, the absorbed energy is increased to great extent when the cool fluid flows through the hot rock blocks, but the temperature of the fluid at the outlet decreases quickly.