The method of imaging spectral angle mapping （SAM） is one of the main methods of mineral spectra identification in imaging spectra image processing technique

but its application result is not very good. The advantages

disadvantages and their causes are studied and discussed in this paper using clustered analysis of similarity coefficients of lithological lab spectra. The test area is located in the Zhaertai Mountain region of northern China. The imaging spectrometer data were collected using the Medium Resolution Airborne Imaging Spectrometer （MAIS） developed by Chinese Academy of Sciences. The paper emphasizes that a spectrum of rock is non linear mixture of minerals’ spectra that include either selective absorption or non selective absorption

and affection of non selective absorption to result of SAM classification. A simple average image is suggested to use in the lithology mapping technique integrated with SAM image

to solve the problem of “different objects having the same spectra” which is often produced in the classification of imaging spectra angle mapping method

thereby obtaining better lithological mapping results.