Abstract: In variable fuzzy algorithm, the evaluation index system is constructed without consideration on influence of the correlation among indexes on the evaluation results and without analysis on the time series variation characteristics of the water resources carrying capacity in the evaluation. To overcome the shortcoming, Principal Component Analysis (PCA) was introduced to select the indexes with low correlation coefficient to construct the evaluation index system. The variable fuzzy algorithm was improved to analyze the time-series variation characteristics of the water resources carrying status in different years. Taking Datong City, Shanxi Province as an example, this paper evaluates the water resources carrying capacity of the city from 2010 to 2017. The evaluation results show that compared with the original algorithm, the stability range of the grade characteristic value calculated by improved algorithm is obviously reduced if under the same evaluation grade and the range of error is reduced and the accuracy of the evaluation grade is improved. The improved algorithm further expands and enriches the variable fuzzy set theory, which has some reference significance for evaluating the water resources carrying status in other regions by the variable fuzzy algorithm.