On the basis of analyzing the deficiency of spectral angle mapper (SAM), an improved similarity measure called weight SAM (WSAM) is proposed in the present paper. The fundamental idea is to set a weight in the "difference range" to increase the discriminability between the similar minerals. When we distinguish some kind of mineral, the authors can find the "difference range", in which the difference in spectral feature between the similar mineral spectrum and the reference spectrum is huge, and gives weight k to the spectrum in this range to reduce the similarity and increase the discriminability between similar minerals. The experiment results of spectra and AVIRIS data indicate that the WSAM method reduces the similarity of target mineral and its similar mineral and increases our ability of visual interpretation.