Background The study on the change of runoff and sediment in the Yangtze River and its causes can provide theoretical basis for mastering the evolution law of runoff and sediment of the Yangtze River.

Methods Based on the measured data of runoff and sediment of Yangtze River's seven major hydrologic stations (Pingshan, Zhuotuo, Cuntan, Yichang, Shashi, Hankou and Datong) and using statistical methods and the double accumulated method, this paper analyzed the changes characteristic and causes of runoff and sediment in Yangtze River during 2000 to 2015.

Results The result showed that the volume of runoff and sediment load of Yangtze River's seven major hydrologic stations decreased. Meanwhile, the volume of runoff did not change significantly, but the sediment runoff changed in a large range. The proportion of the runoff volume of the station in the upper Yangzer River sites in Datong station was small, while the proportion of sediment transport was larger. It indicated that the sediment of the Yangtze River was mainly from the upstream region. There was a significant positive correlation between annual runoff and sediment transport in the sever station site of the Yangzer River. But the correlation coefficient of runoff and sediment transport in Pingshan station was relatively high (R²=0.67), and the correlation coefficients of other stations were low. The double mass curve of Pingshan, Zhuotuo and Cuntan had an obvious turning point in 2010 and 2012, which showed that the sediment load was decreased significantly in the upper Yangtze River the from 2012. The double mass curves of Yichang, Hankou and Datong station had an obvious turning point in 2002 and 2005. The slope was reduced after the turning point which showed that the sediment load was decreased significantly in the middle and lower reaches of Yangtze River from 2002. Moreover, The turning point of Shashi station was in 2002 and 2007 and the amount of sediment has been a certain degree of control after 2007 in Shashi hydrologic station. The annual runoff in the Yangtze River basin from 2000 to 2015 year has not changed significantly, and the trend of runoff and annual rainfall was consistent. The Sediment discharge was on a downward trend, the change trend of the annual precipitation and sediment from 2003 to 2009 was poor consistency, which showed that the precipitation had little impact on the sediment concentration between 2000 and 2015 in the Yangtze River. The reservoir sediment, the soil and water conservation engineering and other human activities are the main reasons that cause Yangtze River's relations of water and sediment changing obviously since 2000.

Conclusions This research could provide the theoretical basis for the protection of the Yangtze River.