Pressure retarded osmosis (PRO) is a promising technology for salinity gradient energy utilization. Here, based on previous literature, we proposed a simplified model to describe the PRO process, which was validated by a great accordance with the experimental data of water flux and power density. A sensitivity analysis of the PRO system indicated that there exist different optimal hydraulic pressure differences leading to the maximum power density and energy efficiency, respectively. The performance of the PRO system under the maximum power density and energy efficiency is systematically investigated based on the GA method. Furthermore, the Pareto front that indicates any arbitrary compromise between the maximum power density and energy efficiency based on NSGA-II was obtained. Factors determining the choice of the final compromise solution in the Pareto frontier remains are systematically discussed, which should be referred to the local energy policies and technical and economic conditions of the PRO systems. For demonstration, the final compromise solution selected by the abstract heuristic TOPSIS method is discussed and a desirable compromise between the power density and energy efficiency is presented.