In order to understand the variations and causes of water and sediment in major rivers in southern China, the variation characteristics of runoff and sediment load at representative stations are analyzed and main influencing factors are investigated using the Mann-Kendall test method and the hydrological accumulation curve method. The results show that the annual runoff at representative stations of the main southern rivers such as the Yangtze River, the Pearl River, the Qiantang River and the Minjiang River has no significant change trend. The annual sediment load at representative stations in the southern rivers has a significant decreasing trend except for the Qiantang River. The Qiantang River experienced a normal runoff and sediment load period from 2016 to 2020, and a normal runoff and high sediment load period from 2011 to 2020. However, the other rivers experienced a normal runoff and low sediment load period from 2016 to 2020 and from 2011 to 2020. The main factors affecting runoff and sediment load include reservoir sediment retention, water and soil conservation measures, sand mining from rivers, and excessive construction. Among them, reservoir sediment retention is the main measure responsible for sediment reduction in southern rivers, water and soil conservation measures play an important role, and sand mining from rivers also plays a certain role in river sediment reduction.