AbstractOrganic Rankine Cycle(ORC) can effectively recover the low grade heat source due to its distinctive thermodynamic performance. Based on Genetic Algorithm, net power output per unit mass of geothermal water is set as the objective function. Evaporation pressure, superheating of the steam, the minimum temperature in the evaporator are analyzed to obtain the optimal performance of the system. The results indicate that under the assumption condition that the optimal level constitution of system parameters is determined as the working fluid of R227ea, the power output of the system of 596kw and the corresponding power output per unit mass of geothermal water of 11.91kJ/kg. R245ca has the maximal efficiency of 5.75% among the selected 6 working fluids (Butane, R236fa, R227ea, R236ea, R245fa, R245ca). The effect of pinch temperature in evaporator on power output per unit mass is more seriously than that of superheating. It is about 7 times in terms of increasing 1K of R227ea.