Based on the data from 27 meteorological observing towers over South China for one year, it is found that the average wind power density index is less than the threefold wind speed index. The variation law between annual mean wind and shape parameter with height and a new method for estimating the average wind energy density at different heights are discussed. The results show that the average relative error of this method is 96%, which provides references for computing the wind power density so to estimate the variation of wind energy with height for the stations without gradient wind observation.