Abstract: ASTER sensor provides 14 bands of spectral information including visible and near infrared （VNIR）, short wave infrared （SWIR） and thermal infrared （TIR） . The highest spatial resolution is 15 meters which lies in VNIR bands. Besides, the stereo imaging of the same area can be obtained simultaneously by the nadir- and aft-looking of 03 N and 03 B bands respectively. Topographic information can then be derived from them by certain algorithm. All these characteristics make it very convenient in geological application. The fault system may cause differences in geology and morphology inside and outside the system. Accordingly, these differences may produce different spectral and textural characteristics in the image. In the reverse, the characteristics can be emphasized by enhancing the difference of intensity and texture by using certain image processing technology. Analysis then can be done on their difference, some tally with certain laws can be regarded as fault system, and its attribute may be concluded. An application of ASTER data in Baiyin area of Gansu province was introduced in this paper. The results show a high consistency with the field survey as shown in the local geology map.