The effects of a 2-D ridge flow field on the mean flow and turbulence structure in the neutral surface layer were numerically investigated by using a non-hydrostatic higher-order turbulence closure model developed in this paper. The influences of the shape of the hill and the surface roughness of ridge on the fluctuation of flow around hill were discussed. The results show that a large discrepance was produced when the hydrostatic assumption was adopted, especially on the mean flow field. When the hill become steeper or background wind speed become larger,this discrepance is more considerable.