根据物元分析原理将单一的决策问题拓展为多维的物元结构，并对传统物元模型中的中点与区间距的计算上进行了改进，采用熵权法确定指标的权重，构建出流域水质评价的改进物元模型。利用广西北之江流域2011年水质数据，选取5个典型断面和8个水质评价指标，采用改进物元模型进行计算，得到综合评价结果为北之江流域上游属II类水，中下游属III类水。该评价结果与来宾市水功能区划分情况基本一致，说明改进物元模型可用于水质的综合评价。

In this study, the matter-element analysis theory was used to expand the single policy decision problem into a multi-dimensional matter-element structure, and the calculation of the distance of point and interval in the traditional matter-element model was improved. The entropy method was used to determine the weight of each index, and an improved multi-dimensional matter-element model of water quality assessment was developed. The improved matter-element model was used to evaluate the water quality in the Beizhijiang Drainage Basin of Guangxi. The water quality data in 2011 were collected, and five typical sections and eight water quality assessment indexes were selected. The results showed that class II water is in the upstream of Beizhijiang Drainage Basin , whereas class III water in the midstream and downstream. The results were in accordance with water function zonation in Laibin city, indicating that the improved matter-element method is reliable for quality assessment.