[Objective] The water quality change characteristics and driving factors of Youjiamao reservoir, which is a drinking water source of mining area in Northern Shaanxi Province were analyzed to provide a technical support for the protection and treatment of drinking water in similar areas.[Methods] The water quality of Youjiamao reservoir was continuously monitored from 2013 to 2019, and 20 water quality indicators were obtained. The principal component analysis (PCA) and PCA-entropy method were used to analyze the monitoring data.[Results] ① Turbidity, chroma, manganese were the main driving factors of water quality in Youjiamao reservoir, followed by permanganate index and ammonia nitrogen. The primary task of water purification was to remove manganese. ② The water quality of Youjiamao reservoir was the worst in 2014, and was better in 2015 and 2016. Water quality was the best in winter and the worst in summer, which had obvious correlation with the precipitation and temperature. ③ PCA was a feasible method to identify the main driving factors of water quality, which was basically consistent with the calculation result of PCA-entropy method.[Conclusion] Manganese pollution is the key factor for the deterioration of water quality in Youjiamao reservoir, and the manganese concentration is significantly higher in summer. Therefore, water treatment technology should be adjusted or chemicals dosage should be increased to meet the drinking water safety.