[目的] 分析黄土高原马莲河干流水质时空变化特征，揭示水质污染状况及成因，为该流域内生态文明建设和水环境治理提供科学依据。[方法] 基于黄土高原马莲河干流2016—2021年甘肃省庆阳市境内5个断面水质逐月监测数据，结合单因子污染指数法、综合污染指数法对水质进行评价，利用线性趋势法对水质演变趋势进行分析。[结果] ①2016—2021年庆阳市境内马莲河水质整体较差，属于Ⅴ类水范畴，综合污染指数较高，主要污染因子为高锰酸盐指数、化学需氧量(COD)、5日生化需氧量(BOD5)、氨氮(NH3-N)、总磷、氟化物及六价铬，下游水质优于上游。②庆阳市境内马莲河干流水质季节变化特征显著，综合表现为夏、秋季优于春、冬季。具体表现为秋季最优，冬季最差。[结论] 2016年以来，庆阳市境内马莲河水质趋势稳定向好，尤其是2017年以后，向好趋势表现明显；受入境水质及流域地质条件影响，马莲河水污染治理任务依然任重而道远。
[Objective] The temporal and spatial variation characteristics of water quality in the main stream of the Malian River in the Loess Plateau were analyzed in order to reveal the pollution status and causes of water quality, thereby providing a scientific basis for the construction of ecological civilization and improvement of water quality in the basin. [Methods] Monthly water quality data from 2016 to 2021 for five sections of the mainstream of the Malian River at Qingyang City of Gansu Province in the Loess Plateau were evaluated by using the single factor pollution index method and the comprehensive pollution index method. Trends in water quality evolution were analyzed by using the linear trend method. [Results] ① The overall environmental quality of the Malian River water in Qingyang City from 2016 to 2021 was poor (category Ⅴ), and the comprehensive pollution index was high. The main pollution factors were permanganate index, chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), ammonia nitrogen (NH3-N), total phosphorus, fluoride and hexavalent chromium. Downstream water quality was better than upstream water quality. ② The seasonal variation characteristics of water quality of the mainstream of the Malian River in Qingyang City were significant. The comprehensive performance was better in summer and autumn than in spring and winter, and the specific performance was best in autumn and worst in winter. [Conclusion] The trend of the water quality of the Malian River in Qingyang City since 2016 has been stable and improved, especially after 2017. Due to the influence of the water quality of the water entering, the river and the geological conditions of the river basin, the water pollution control task for the Malian River still has a long way to go.