On the basis of caloric balame and eddy diffusion

H. L. Penman presentedthe Calculating formula about free water surface evaporation under the condi-tion of non advection water vapour transport. Although Penman's formula hascertain theoretical basis

it doesn't consider the influence of changes in heat storage of water body on evaporation quality. On the other hand

H. L. Penm-en uses area empirical formula to calculate radiative equilibrium value and"Drying Force" Ea. It has not been proved yet whether panman's formuleis available to the arid area in China. This ariticle is trying to test and revisePenman's formula with the data which come from 20 m2 evaporating poolmeasurement in evaprating experimental station at Hadipo in Xinjiang

Theaccuracy of monthly water surface evaporation quality will be improved withthe revised penman's formula.