The flash-binary system includes the single flash power system and the binary cycle system. The flash-binary power system enhances the production as compared with the single flash power system. In addition, compared with the two-stage flash power system, the single flash-binary power system can avoid some problems, such as the bulky equipments, the difficult installment and the high cost. Based on the numerical simulation, the effect of the geothermal water temperature on the net power output, the thermal efficiency and the optimal temperature of the flash-binary power system are discussed in this paper. The simulation results show that, when the temperature is 80℃, the net power output per geofluid is about 1.08 and 0.86 kW·h/t by the direct cooling and the indirect cooling of the flash system, respectively; when the temperature is 150℃, the values are 6.57 and 6.35 kW·h/t; when the geothermal water temperatures are 100, 130 and 150℃, the optimal temperatures of the combined system are 80 and 85℃, 100 and 115℃, 125 and 140℃ by the direct cooling and the indirect cooling of the flash system, respectively. In addition, the power output of the flash-binary system by the direct cooling is dominated by the flash power generation, while that by the indirect cooling is dominated by the binary power generation. The flash-binary power system could provide a technical support for the geothermal resource utilization in China.