Hunan Province launched the second “Three-year Action Plan” for protection and treatment of Xiangjiang River from 2016 to 2018. However, restoration effect on water quality of Xiangjiang River and key factors were not entirely clear. In this study, daily water quality monitoring data from 26 water quality monitoring stations in the main stream and tributaries of Xiangjiang River from 2015 to 2018 were selected to analyze impact of action on water quality changes in the Xiangjiang River. The results showed that water qualities indexes remained above class III of national surface water during the investigation period. Temporal and spatial variations were as follows: ammonium was accumulated while total phosphorus was elevated and then declined along the trunk stream. The pollution of tributaries was more serious than that of main stream, and ammonia nitrogen concentration was lower and total phosphorus concentration was higher in rural stations than in urban stations. Ammonia nitrogen concentrations was high in winter and low in summer, while concentrations of total phosphorus peaked in autumn. Water pollutants were negatively related with pH and dissolved oxygen, but positively correlated with CODMn. The main possible sources of ammonia nitrogen and total phosphorus were industrial and agricultural emissions, respectively. Due to the Action, ammonia nitrogen, total phosphorus, and potassium permanganate index reduced by 32.24%, 30.03% and 5.80%, respectively, while dissolved oxygen increased by 4.66%. These mitigations were primarily contributed by collaborative control of nitrogen and phosphorus in industrial emissions along trunk stream, and followed by agricultural source emission reduction in villages and tributaries. Therefore, future protection and treatment of Xiangjiang River system should be more focused on the discharge of agricultural pollutants, especially phosphorus.