Abstract: In gauge and research work on coefficient of evaporation and heat dissipation of water Surface，the author discovered the existence of a conside-table error on humidity in the Evaporation Experience Formula of Dordon．
There is discrepancy from the fact using in his formula（ e₀-e_a ）to reflect the humidity of air，since the saturation pressure of vapour，which is indicat-ed with "e₀"，corresponding to the temperature of surface water（ Ts ）is unequal to the vapour pressure corresponding to the temperature of air on the surface of water（To）．Therefore，if using the difference of saturated vapour pressure indicated by（e₀-e_a）to substitute the actual difference of saturated vapour pre-ssure，there would come out the error．
The author put forward in this article to amend the formula with relative humidity．After testing it is proved that the nevised formula can offer a satisfying result．