In this paper,turbulent flux over canopy of field crops was calculated using Profile Gradient Method derived from Monin Obhov Similarity Theory and drag coefficient,Stanton number and Dalton number were also further defined.The applicability of universal function which was used for turbulent flux calculation was examined and whether or not the flux and drag coefficient varied with atmospheric stratification stability,roughness length and average wind speed was discussed.Results of the study indicate that the flux depends on the stability and the drag coefficient,the Stanton number or the Dolton number is pertain to the stability,roughness length and average wind speed respectively.