Factors influencing the runoff and sediment changes of the Yangtze River are numerous, and the human activities are affecting the water and sediment movement more and more obviously besides natural factors. Runoff and sediment changes of the Yangtze estuary are influenced by both natural and human activities. This paper uses the Mann-Kendall method to analyze the monitoring information for the current decades at Datong station. The results show that the annual sediment transportation decreases in recent decades at Datong, especially obviously from 2003. The sediment reduction of the Yangtze estuary is mainly due to the significant reduction of sediment supply in the Yangtze River basin, which is caused by the sediment retention by reservoir engineering, soil and water conservation engineering in the upper Yangtze River, sand mining, and sedimentation at the middle reaches in the Yangtze River, etc. It’s obvious that the south branch and outlets delta are scouring recently because of the sediment reduction in the Yangtze estuary. More attention shall be paid to this change.