The Honghuatao-Gulaobei section located at the exit of the upper stream of the Yangtze River was selected for this study. Comparison of grain size over 1mm of gravels in the first terrace with that of modem Yangtze River bedload and slack-water sediments of modem floods with that of paleofloods show that hydraulic power of the large floods of more than 30000 years ago was 1.5 times stronger than that of modem floods in the Yangtze River. Comparison of grain size over 80mm of gravels in the first terrace with that of modem Yangtze River bedload and slack-water sediments of modem floods with that of paleofloods show that hydraulic power of the large floods of more than 30000 years ago was 1.35 times stronger than that of modem floods in the Yangtze River. It suggests that the magnitude of floods 30000 years ago could be much larger than those of the modem Yangtze River.