There is a lot of various spectrum curves and data in geoscientifical investigation. It is impossible to research and compare the original spectrum curves directly,because there are so many of them and they are much too complex. We have to find out methods to change them into simple indexes for practical use, but not losing any important research information. The original spectrum curves convey research informations of two main aspects:(1)overall radiation intensity described by the curve position,high or low;(2)internal relationship between different wave bands described by the structure model of the curves. The overall intensity can be influenced strongly by change of external conditions during measurement,but not the internal relationship,because which is determined by chemical composition and material structure of the observed object. This paper introduces a method to simplify complex original curves into simple spectrum indexes, not only for the advantage of practical use,but also for the purpose of obtaining more reliable research information by enhancing the internal relationship and weakening the overall intensity. With this method one gets a set of four spectrum indexes:spectrum coefficient x and y,dominant wavelength λd,as well as spectral purity Pe.