According to the long time series observation data of monthly runoff and sediment, annual variation law and its causes of runoff and sediment flowing in and out of the Dongting Lake were analyzed by means of non-uniformity coefficient, concentration degree and concentration period, and the Mann-Kendall trend test methods. The results showed that: Annual runoff distribution of the four Rivers (i.e., the Xiang River, Zi River, Yuan River and Li River) into the Dongting Lake were uneven, the concentration period was from May to July. Annual sediment distribution were very uneven and had a trend of being more and more uneven, the concentration period was from June to July; Annual runoff distribution of three oulets of Jingjiang into the Dongting Lake changed little in general trend, but the annual distribution of sediment were more and more uneven, the concentration period of runoff and sediment were both July; The CVy values of annual runoff and sediment in Chenglingji differed for different years, CVy values of annual sediment fluctuated and had increase trend, but there was no trend for CVy of annual runoff; the concentration period of runoff was in July, but the concentration period of sediment was in April due to the interaction of runoff and sediment; Annual distribution of runoff and sediment became more uniform because of the application of the hydraulic engineering construction and conservation of water and soil. The concentration period of runoff and sediment for the four rivers, three outlet and the lake delayed gradually, the concentration degree of sediment was higher than runoff.