A first-order closure model is presented to describe the canopy flow. The momentum transfer equation is derived on the basis of a spatial average scheme. Prandtl’s mixing length model is modified to take into consideration of the canopy geometrics by comparison of eddy movement to radiation transfer. The function of leaf angular distribution used frequently in foliage radiative transfer theories is adopted in the derivation of the model and in the evaluation of its coefficients. The dimensionless forms of the model suggest that the canopy flow structure is controlled by three dimensionless coefficients, namely, canopy dragcoefficient BT (defined as BT=1.4Φ√v√uHw, where Φ=5, uH denotes windspeed at the top of the canopy and w leaf width), dimensionless leaf area distribution ao and leaf area index LAI, the latter two of which determine the canopy geometrics.Coefficients in the model are evaluated theoretically. Inputs required by the model are w, a_n, uH and LAI. The validity of the model is supported by the experiment on a maize stand by J.D. Wilson and others. Influence of BT, a_n and LAI on canopy flow is discussed numerically. The fitted exponetial extenuation coefficients AFU of windspeed within the upper part of the canopy are illustrated by a figure.