Desalination of seawater has been considered as one of the most promising techniques for supplying fresh water in the regions suffering water scarcity. Reverse osmosis (RO) is one of the major technologies for mid- and large-size desalination plants because it offers a means of producing high quality of water from seawater with lower energy consumption than other processes such as evaporation processes. In this study, RO systems for seawater desalination were theoretically investigated to provide insight into the optimum process design. A simple model based on the solution-diffusion theory and Multiple fouling mechanisms was developed and used to analyze the performance of RO systems. The effect of recovery ratio and permeate flux on the efficiency of the whole RO system was investigated for a wide range of operating conditions. The model was also applied to optimize the design of RO process for low energy requirement and high boron removal.