Based on the average monthly runoff records from 1950 to 2000 at Datong station of the Yangtze River, the Mann-Kendall trends test has been applied to examine the runoff trends in the lower reaches of the Yangtze River. The results show the average discharge in the 1990s was the highest, in comparison to other decades for Datong station, and there is a slight increasing of runoff in the lower reaches of the Yangtze River from 1950s, the trend will be continued due to the effect of global wanning. As to seasonal and/or monthly variation, a distinct decreasing trend has been detected for autumn, and there is significant increasing trend in summer and winter, especially in winter. In some sense, the increasing of runoff for winter may mitigate the pressure of the environments at the delta of Yangtze River. Significant positive trend has been observed for flood seasons and dry seasons, which is more obvious in dry seasons. The increasing of runoff in 1990s is very closely linked with the global warming, quicker water circulations and the increasing of precipitation in the Yangtze River catchments.