Based on considerations of the relationship between the evapotranspirationand the humidthermal conditions,a new connexion equation of heat and waterbalances has been developed:E=(R/L)e^m(R/Lr) Where E is the mean annual evapotranspiration;R,the annual radiation balance;r,the annual precipitation;L,the latent heat of evaporation;and m,anempirical coefficient.The results obtained from calculating the annual values of evapotranspirationfor some stations in the Yellow River Basin and South China by the new equation,as compared with those calculated from water balance data,are similar andacceptable.As conclusion,the application of the new equation to hydrological practicesis found to be reasonable.