After the operation of the Three Gorges Reservoir, the intensity of bank collapse has significantly increased in the middle and lower Yangtze River, in which bank collapses show concealment and suddenness, making the quantification and assessment of bank collapse challenging. Three typical reaches, Xiangjiazhou, Qigongling, and Chengdezhou along the middle and lower reaches of the Yangtze River were selected. Based on multi-source remote sensing images and topographic data, the indicators for quantifying bank collapse were analyzed, including bank-slope ratio, elevation difference of the beach-trough, erosion degree of the slope toe, ratio of the distance from the bank to channel width, and bankline change. Thresholds for these five indicators were quantified, and the fuzzy analytic hierarchy process was used to determine the weights of the indicators. The results indicate that the ratio of the distance from the bank to channel width and bankline change are the primary factors influencing bank collapse, with weights of approximately 0.40 and 0.25, respectively. The bank-slope ratio, elevation difference of the beach-trough, and erosion degree of the slope toe are the secondary factors, with weights ranging from 0.10 to 0.15. The threshold values for the indicators of bank collapse differ among the various reaches: the bank-slope ratio and the erosion degree of the slope toe for Xiangjiazhou are 0.04 and 0.10, respectively; 0.50 and 0.16 for Qigongling; and both are 0.2 for Chengdezhou. In all three reaches, the elevation difference of the beach-trough is over 15 m, the threshold for bankline change is between 0 and 0.5 m, and the ratio of the distance from the bank to channel width is between 0.3 and 0.4.