地质研究对象的各种波谱曲线和数据包括显示量(由曲线的高低位置反映的总体辐射强度)和质(由曲线内部的起伏结构反映的不同波段辐射强度的内在相互关来)两方面的特征。其总体辐射强度往往因各种观浏因素和条件的不同而发生变化，但其曲线结构型式却一般不会因此而改变。本文一般性地介绍一种将复杂的原始波谱曲线简化成简单指数的思路和方法，使各种波谱曲线所反映的物体内在本质特征得以加强突出，同时尽量弱化总体辐射强度这一易变的量的特征。

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.