Abstract: The integration of water-reusing system leads to intensive interactions among processes.The flexibility of the system can be improved by changing the water network structure.Regarding the water-reusing network system with multi-contaminants, the flexibility of the system was analyzed in this paper.Two indices, namely additional process control number and process connection number, were put forward and adopted to evaluate the flexibility of the system simultaneously.A stepwise mathematical model was proposed to minimize the amount of fresh water consumption,and optimize the additional process control number and process connection number of the network.In a case study on the water-reusing system with multi-contaminants, the feasibility of the model established in this paper is verified after the water reusing network that has the least amount of fresh water consumption as well as the smallest additional process control number and the smallest process connection number is realized.