Through field investigation on wind speed,aerodynamic roughness,rate of sand transportation,and structure of wind-sand flow on different underlying surfaces,we found that vegetation cover can effectively prevent soil erosion by wind.In comparison of the fixed sandy land of 40% vegetation coverage with the drifting sand dune without coverage,the average wind speed at the height of 0.2 m was reduced by 43%,the successive time of threshold wind velocity for soil erosion was reduced by 85%,the threshold wind velocity for soil erosion was increased by 70%,and aerodynamic roughness was increased as much as 180 times.Compared with the drifting sand dune,when the speed of wind-sand flow is similar,the rate of sand transportation on the semi-fixed sandy land was reduced by 62.33%,while fixed sandy land,by 93.07%.The results indicate that a single plant can also reduce wind speed.Two single Artemisia ordosica can reduce wind speed at the height of 0.5 m by 59.4% and 19.8%,respectively.