Abstract: The applicability of the similarity theory in the surfacelayer is studied by using the gradient observations of fluctuation and mean fields. The study results show that the approximation of constant fluxlayer can not come into existence basically in the surface layer over vegetation land. The decreases with height significantly. The increases about 50% with height within 12m over surface. The heat fluxcalculated by the profile-flux method represents the mean value within some heihght.