Abstract: A new design method for effluent treatment system with a single contaminant is presented. The method consists of one principle and three rules. The key point of the method is that global optimality is obtained by guaranteeing the optimality of each step taken in the design procedure. The costs per unit mass of removed contaminant is used as a scale to choose the next combination of an effluent stream and a treatment process. The remaining problem is updated after each choice. After a primary distributed network without stream mix is obtained,the rules are used to further improve the structure.Comparing with the present targeting and mathematical programming methods, the new method is simple and effective.