in this paper the cost of small reverse osmosis unit is discussed. Based on the analysis of energy consumption model we get the RO cost model which restricted by the operating conditions. Analysis the relation between independent and dependent variable use correlation analysis method in SPSS. The results show that the operating pressure, water flow, water concentration, inlet water temperature has the strong linear correlation with water flux, and also has the linear correlation with energy consumption. From the model that the change of operating conditions will cause dis- posal expenses change, Control the operation condition can realize energy consumption. The model result can be used as the next stage that study the boiler water supply optimizes in power plant under uncertain conditions.