To study the water quality characteristics in the coal-antimony concentrated mining area of Qianxinan Prefecture, Guizhou Province, water samples were collected along two adjacent karst underground rivers, Longbaiwei and Shuiya. The hydrochemi-cal characteristics of groundwater in the study area were analyzed using Piper trilinear diagrams, Gibbs models, and ion ratio diagrams. A fuzzy comprehensive evaluation model based on the CRITIC method and the analytic hierarchy process (AHP) was applied to assess the water quality of the two karst underground rivers. The analysis results show that longbaiwei is mainly dominated by HCO₃-SO₄-Ca type water. In contrast, Shuiya is primarily dominated by HCO₃-Ca and SO₄-HCO₃-Ca type water, with the hydrogeochemical evolution mainly controlled by carbonate rock weathering. Nine factors, including Fe, Mn, , and Sb, were selected as evaluation indicators. The water quality of the two adjacent karst underground rivers was assessed using the fuzzy comprehensive evaluation method. The evaluation results show that 20% of the water samples from Longbaiwei are categorized as Class Ⅲ ~ Ⅴ, indicating unsuitability for drinking, while the water quality of the Shuiya underground river is better than that of the Longbaiwei underground river. Comparing the evaluation results, it is evident that the concentrated mining of coal-antimony has led to a large amount of mine drainage entering the karst underground river system, resulting in excessive concentrations of ions such as Fe, Mn, , and Sb. However, the degree and extent of pollution vary significantly due to differences in hydrogeological conditions, karst development status, and the scale of surrounding mining areas.