In the geothermal heat organic Rankine cycle power generation system，condensation temperature is sensitive to the environment condition while the geothermal fluid parameters remain constant.In this paper simulation of the ORC system is carried out through the EES software to analyze the effect of the condensation temperature in a saturated organic Rankine cycle power generation system using R245fa and R601a as working fluid.The optimal expansion ratio，mass flow rates and the inlet temperature of the expander are also studied.The results show that，when the temperature of the geothermal fluid is kept at 130 ℃，the optimal working fluid temperature at the expander entrance increases by 15 ℃ with the condensation temperature decreasing from 30 ℃ to 0 ℃.At the same time，the system net power output growth by 120%，refrigerant mass flow rate increases more than 30%，and the expansion ratio becomes approximately 2 times higher.This leads to higher requirements on the initial system design and control.