Abstract: New Reynolds mean momentum equations including both turbulent viscosity and dispersion are used to analyze the vertical profile of wind speed in surface layer.It is pointed out that the wind profile of surface layer including turbulent dispersion is a power + logarithmic law,and under the neutral stratification, it is transformed into logarithmic,but the von Karman's constant k is replaced by k₁=(1+k/4)^-1k;under unstable stratification the effect of dispersion is stronger than under stable.In the light of the similarity theory the same constant is obtained.