In this paper, cycle efficiency, net electric power and steam lose rate are calculated between the single flash and binary geothermal power system. The prime mover is 10kW single screw expander. These parameters of the single flash system are calculated by rated inlet volume flow rate of the single screw expander. The heat absorption capacity of both systems is determined to be equivalent. The working fluids of binary system are R134a, R245fa, and R600a. Those parameters of binary system are calculated with the condition that the saturated temperature of the working fluid before pump is 22°C. Engineering Equation Solver (EES) software is used for analysis. The results show that electric power of the single flash system is on the rise and steam loss rate of the single flash system is on the decrease with an increase of the inlet temperature between 100°C and 155°C. From the same heat absorption capacity, the binary system has apparent improvement in electric power and efficiency. The efficiency of binary system can increase by 2.1% compared with single flash system.