The Enhanced Geothermal System (EGS) is a recognized geothermal exploitation system for hot dry rock (HDR), which is a rich resource in China. In this study, a numerical simulation method is used to study the effects of geothermal fluid dryness and non-condensable gas content on the specific enthalpy of geothermal fluid. Combined with the organic Rankine cycle (ORC), a numerical model is established to ascertain the difference in power generation caused by geothermal fluid dryness and non-condensable gas content. The results show that the specific enthalpy of geothermal fluid increases with the increase of geothermal fluid temperature and geothermal fluid dryness. If the dryness of geothermal fluid is ignored, the estimation error will be large for geothermal fluid enthalpy. Ignoring non condensable gas will increase the estimation of geothermal fluid enthalpy, so the existence of the non-condensable gas tends to reduce the installed capacity of a geothermal power plant. Additionally, both mass flow of the working medium and net power output of the ORC power generation system are increased with increasing dryness of geothermal fluid, however there is some impact of geothermal fluid dryness on thermal efficiency.