Reverse osmosis (RO) often used for desalination, in producing the ultrapure water for electronics, pharmaceuticals and power generation industries and also it was used in small niche process such as food processing and pollution control. Analysis of membrane performance required multiple of experimental run. Experimental work can be time consuming and costly. Hence, this work aims to model a small scale RO system by using a solution-diffusion model to minimize the experimental work. The model was verified by comparing the data obtained from the model and experimental data. Other studies, which include, the influence of solute feed concentration on the RO system was also been investigated. A commercial RO Trisep flat sheet membrane was used. The solute permeate concentrations, solvent permeate flux, final solute feed concentrations and rejection rate of sodium chloride (NaCl) was analyzed to observe the membrane performance. Result shows that some experimental data has almost similar trend with the simulated data. Both solute feed concentration and rejection rate of NaCl over time show almost similar trends with percentage errors are 8.89% and 0.76% respectively. As solute feed concentration increased, the solute permeate concentration increased. In contrast to the solute permeate concentration, when the solute feed increases the solvent permeate flux decreases and rejection rate will also decrease.