Abstract: Through the exergy analysis of heat-exchange process, the author in this paper has derived the calculation formilae of exergy low(ΔE) & exergy efficiency under the circumstances of cosidering heat exergy low and flow exergy low simultaneoraly. the results show that there is a possible esistence of the limit point ofΔE. when load of heat-exchanger (Q)is constant. To make use of exergy of heat-exchanger as much as possible，the diameter of heat-exchanger and the flow rate of cold & heat fluid should be appropriately matched.

Key words: heat-exchanger, thermodynamic system, exergy analysis