Abstract: This paper presents a new superstructure model of heat exchanger networks with stream no -splitting based on ranges of stream supply temperatures and the method of simultaneous optimal design of flexible heat exchanger networks synthesis. Firstly, the streams with ranges of supply temperatures are parted. Secondly, a superstructure model of heat exchanger networks is proposed based on rules, and the simultaneous optimal mathematical model of flexible heat exchanger networks synthesis is established. Thirdly, the genetic algorithm is applied to solving the mathematical model established at the second step effectively. Finally, the parting streams are merged and the load of heat exchanger is relaxed , and optimal flexible heat exchanger networks configuration can be obtained very easy. Some case studies demonstrate that the method is effective.