In order to find out the water quality of the Sibao Reservoir in Jiangmen City, water samples were collected and tested seven times from 13 sampling locations in June to December 2018 to analyze the temporal and spatial variations of water quality factors. The water quality and eutrophication of Sibao Reservoir were evaluated using the single factor evaluation method, BP neural network, principal component analysis method and index method. The Pearson method was used to study the correlation between chlorophyll a and water quality factors, and to analyze the main driving factors affecting reservoir eutrophication. The results indicated that the changes of total phosphorus, total nitrogen and ammonia nitrogen in different months were relatively complicated. The water quality near the middle and lower reaches of the reservoir was better, and that in the catchment area was poorer. The results from the single factor evaluation and BP neural network were consistent, indicating that the water quality of the reservoir was generally between class III~IV. The principal component analysis showed that the water quality was mainly affected by permanganate index, total phosphorus, total nitrogen and ammonia nitrogen. The results of the index method showed that the reservoir was in a state of mild eutrophic, and the degree of eutrophication in the catchment area was higher. The correlation analysis showed that chlorophyll a had strong correlation with ammonia nitrogen and permanganate index. Nitrogen was the limiting factor for the growth of phytoplankton, and the control of nitrogen concentration could effectively control the eutrophication of water bodies.