Surface water was used as raw water for the reverse osmosis system in an chemical plant.Since biological pollutants exist in surface water,serious blockage has ocured in the reverse osmosis system as a result.According to the operating problems resulted from the surface water quality,how to solve the problems such as improving pre-treatment system,eliminating defect of hidden devices,strengthening online cleaning and adding proper chemical agents synchronously was introduced.Finally,the reverse osmosis system can work normally.