Based on topographies from 2004 to 2014 and using the Kring interpolation method and mathematical statistics method,we analyze the morphological evolution of Sitan reach and illustrate the scouring-erosion variation characteristics of channel. We also analyze the influence of the discharge and sediment variation and channel regulation upstream on the morphological evolution. The results show that the overall Sitan reach is in the state of erosion from 2004 to 2014,during which the scouring is severel from 2007 to 2013. The analysis shows that the main reason for the undercutting of riverbed from 2004 to 2014 is the sharp decrease in sediment discharge from upstream due to the construction of more and more dams. The sand blocking effect by Changzhou Dam since 2007 and the channel regulation project from 2008 to 2010 are the main reasons for the sharp erosion during 2007 and 2013. The river bed undercutting leads to the lower water level but will not affect the navigation depth.