The Chenghan reach is undergoing considerable channel degradation, and significant bank retreat processes have occurred at local sites due to the operation of the Three Gorges Project (TGP). The adjustment process of cross-sectional profiles in the Chenghan reach was investigated quantitatively by adopting the reach-average method and using the measured topographic and hydrological data after the TGP operation. It mainly covers the adjustment of bankfull channel dimensions and the relationship between these bankfull variables and the previous flow-sediment conditions. These results indicate that the bankfull channel width in the Chenghan reach increased from 1710 m in 2003 to 1732 m in 2016, with an increase of 1.28%. The bankfull channel depth increased from 16.47 m in 2003 to 17.95 m in 2016, with an increase of 9.0%. The channel adjustments in the subreaches of Bailuoji, Jiepai, Jiayu, Paizhou and Wuhan were mainly characterized by an increase in bankfull depth. The channel adjustments in Luxikou subreach behaved to have an increase in both depth and width. The average annual bank-erosion rate of the Chenghan reach from 2006 to 2016 was 5.5 m/a, and the cumulative bank-erosion length of 19.6 km accounted for 8.3% of the total length of the bankline, with 55.3% of the bank-erosion regions located at the right bank. The bank-erosion regions in the Paizhou subreach accounted for 75.9% of the total length of the retreated bankline in the Chenghan reach. Various factors influencing bank retreat in the key subreach of Paizhou have been presented, and the results indicate that the sediment hydrograph is a dominant control factor, and localized bank collapse depends on channel boundary conditions. Finally, empirical relationships were developed between the section-scale bankfull width at typical section with severe bank collapses and the average fluvial erosion intensity during flood seasons in previous years. The proposed empirical relation can consider the effect of the altered flow and sediment regime on the variation in bankfull width at a typical section.