Based on observed dada in 2005 over Dingxi station in semi-arid region of Northwest China, aerodynamic roughness length is estimated, the temporal variable and the relations with wind speed and vegetation density are also analyzed. Combined with LAI from remote sensing, aerodynamic roughness length is simulated by using aerodynamic model. The results show that:（1）Aerodynamic roughness length is on the contrary to wind speed trend. With vegetation density increasing, roughness length will be increased.（2）The effect of vegetation density and LAI on aerodynamic roughness length is large with individual plant height more than 0.2m, and wind speed effect on aerodynamic roughness length is large when individual plant height is less than 0.2m. (3)The relation and the model of aerodynamic roughness length with LAI, vegetation density and wind speed is put forward by combining with LAI from remote sensing, the model can reflect real status, and equivalent vegetation density is presented by using LAI in the model, which is an available means to parameterize aerodynamic roughness length from remote sensing.