Abstract: Through the analyses on 42 rice field canopy spectral samples,15 soybean field canopy spectral samples and 15 reed field canopy spectral samples, some conclusions were made. The average spectrum of rice is less than that of reed, which is less than that of soybean. The shape of average spectrum of the first derivative of rice is similar to that of reed and soybean. The average spectrum of the first derivatives of rice is less than that of reed, which is less than that of soybean at 528nm, and in wavelengths between 700 and 760nm, rice has two peaks at 705nm and 728nm and one valley at 715nm, and reed only has one peak at 725nm, and soybean only has one peak at 705nm. In wavelengths between 360 and 963nm, the shape of average spectrum of the second derivatives of rice is similar to that of reed and soybean. In wavelengths between 1086 and 1150nm, the shapes of average spectrum of the second derivatives of rice, reed and soybean are different. In wavelengths between 1086 and 1113nm, the rice and reed only have a single peak, and the soybean has double peaks. In wavelengths between 1113 and 1150nm, the rice and soybean only have a single peak, and the reed has double peaks. Then, the function of the significant peaks and valleys of the first and the second derivative spectra of rice and reed and soybean on the distinction of three plants is stated.