Abstract: A nonlinear programming model to systematic syntheses of minium cost networks of exchangers, heaters and coolers is proposed. The strategy of the two-level was considered to solve this model. In the first, the discrete variables are determined using heuristic decomposition and enumeration algorithm. In the second level, the optimization of continuons variables of the network is performed solving a larg scale nonlinear programme. As a search method of nonlinear programme, the modified Box's Complex method has been successfully applied. The method presented here is suitable for design problems of the practical complex heat exchanger systems and has several distinctive advantages. The result has been commercialized.