The influence of alfalfa canopy spectral reflectance caused by wind are analyzed in detail, the spectral reflectance averaging 1.5Hz. Obser. tion indicates that generally the spectral reflectance is much smaller under windy conditions than under calm conditions. Deviations of the reflectance vary with wavelengths. Probabilities of relative deviations greater than 3% are. 80% in TMA and TMB bands, 100% in TMC band and 60% in TMD band. The effects of wind on spectral reflectance of flexible canopy are so complicated that the errors caused by wind cannot be eliminated by using simple methods for determining the mean or medium values. Some vegetation indexes, such as brightness, greenness, redness and yellowness, are sensitive to wind and are not suitable when used under windy conditions. So the standard deviation vegetation indexes are recommended for windy areas.