Mass reduction strongly contributes to reduce the cost and promote the performance of spacecrafts. During the design of spacecrafts, mass minimization for the heat exchanger networks (HENS) is a fundamental and attractive issue for which series of global optimization methods based on numerical simulation have been applied. However, among the existing methods, there is not yet a theoretical method. To develop a theoretical approach, we introduce the concept of entransy dissipation in this work, analyze the entransy dissipation of each heat transfer process and eventually derive the expressions of the total entransy dissipation in the heat exchanger networks, which helps to establish the direct theoretical relation between all the design parameters, i.e. the areas of radiator and heat exchangers and heat capacity rates of each fluids, and the known conditions, i.e. the released heat and inlet temperature of fluid. With the relation, the optimization problem is successfully solved with conditional extremum model. Finally, through the application in a typical heat exchanger network, we prove the optimized total mass to be the least, and find that: (1) the total mass increases with the released heat; (2) the working fluids with larger rho c(p)(3), lead to less mass and energy consumption of HENs. (C) 2012 Elsevier Ltd. All rights reserved.