Abstract: The new method of thermodynamic calculation （the contrast model method） for air-air crossflow wet heat exchanger with wet air condensing first at the entry is proposed in this paper. The contrast model equations are made from the actual heat exchanger equations and the imaginary heat exchanger equations, and than it may be proved that the enthalpy efficiency of the contrast model equations is similar to the temperature efficiency of the dry heat exchanger. So the thermodynamic calculation methods for dry and wet heat exchangers can be unified under given conditions. ....... ..