Through the field observation and the wind velocity measurement, we studied the flow field characteristics at the protection system of vegetation, which was located at K404 of Yulin-Jingbian Expressway, where the wind direction was NW-SE. There is a significant correlation between wind velocity and the topography. The magnification ratio of wind velocity is positive at the windward slope of the moving sand dune and fixed sand dune; the magnification ratio of wind velocity is negative at the leeward slope, which doesnt produce backflow and the wind velocity is reduced as a whole. The characteristics of magnification ratio of wind velocity show that more close to the land, the bigger the wind velocity changes. There is an index function relation between absolute value of wind velocity magnification ratio and vertical height. There is no relation between wind velocity magnification ratio and the types of dunes. The wind velocity closed to the highway decreases significantly, which means that the vegetation protection system can remit the damage of drift sand. The wind velocity profiles over windward slope of the moving, semi-fixed and fixed dunes conform to logarithm law basically, but the wind velocity profiles over the summit and the leeward slope deviates from the logarithmic curves. The aerodynamic roughness of the fixed dunes is higher than that of the moving dunes.