Distinguishing and converting mineral ingredient and content based on the spectrum unmixing of rock are an important direction of high-spectral remote sensing. The thermal infrared spectrum of a block of alkali feldspar granite is measured by using Turbo FT portable infrared spectral radiometer in outdoor site and normal temperature, and the thermal infrared spectrums (7—14μm) of four mineral ingredients of the rock, that is, potash feldspar, plagioclase, white mica, and quartz are also measured under three different conditions, i.e. grain sample of 0.71—1mm in outdoor site and normal temperature, grain sample of 0.71—1mm in indoor site and 80℃, and block sample at outdoor site and normal temperature. Then the spectrum of the rock is linearly decomposed by using the spectrums of the four minerals as the end members, and the results are compared with the results that the ASU spectrum is used as the end member. The result shows that the unmixing effect is best when the spectrums of rock and the end member mineral are measured in the same condition; and that the spectrum of block rock could be decomposed by the spectrums of block minerals, however it could not be decomposed by ASU spectrum. The experimental result is beneficial to the remote sensing geology and mineral mapping.