Abstract: The complexity of the dynamic characteristics of plate-fin heat exchangers is the existence of fin conduction between channels.The steady-state and unsteady-state conduction of fins was analyzed,and a general dynamic model of multi-fluid plate-fin heat exchangers including separator sheet’s heat-capacity was developed.The mathematical model,in partial differential equations,can also be expressed by the form of dynamic thermal resistance network of plate-fin heat exchangers.By the transformation of the dynamic thermal resistance network,the model was represented by algebraic equations of a tridiagonal matrix which can be solved easily and quickly.By using this model,the dynamic responses of both two-stream plate-fin heat exchanger and four-stream plate-fin heat exchanger were preeicted for fluid flow,or inlet tempeatue petubations.The calculated results were in good agreement with test data．