The ratio processing is one of the methods exhancing the landsat images. Bymeans of an analysis of the ratio method with the mathematical concept and themathematical model, the authors consider that the ratio image is not related tothe illuminance (I), sun elevation (E), normal line verctor of the ground (Q) anddiffuse light (D), but only bound up with the ground reflectance. Therefore, it ispossible to apply the ratio image in distinguishing the characteristics of a geolo-gical body on the ground. The authors think that it is necessary to make an atmo-spheric correction before ratio processing. The paper presents the ratio effectiveness in finding mineral image abnor-malities with some examples which have been worked out by the authors.