Abstract: A principle of synthesis of heat exchanger networks using dual approach temperatures has been investigated. According to this principle the excess energy is permitted to across the psuedo pinch point during synthesis without violating the minimum energy cosumption, therefore, to divide a pinched task at pinches into threshold subtasks is not necessary, and this will reduce the heat exchanger units and stream splits, makes the synthesized networks featuring simpler and cheaper. Based on above meantioned principle, an automatic computer algorithm is presented by authors, it can be applied to synthesize heat exchanger networks in industrial scale. The examples show that the networks synthisized by using authors' method are simpler and cheaper than the networks synthisized with pinch design method, and the annual costs of networks are very close to the cost targets.