Bank erosion in the seasonally frozen river (SFR) is subject to the coupling effects between hydrodynamic forces and frost heave/freeze-thaw, and the mechanism is complex. Bank erosion plays an important role in channel evolutions of the SFR. Taking the downstream near dam section of the Dadingzishan Navigation and Hydropower Project in the mainstream of the Songhua River as an example, a bank erosion model coupling hydrodynamic forces and frost heave/freeze-thaw interaction was developed. Bank erosion and fluvial processes in this typical SFR were simulated by the numerical model. The results indicated that the lateral erosion at the bank toe was mainly controlled by hydraulic forces. The cracking depth of the riverbank increased due to the frost heave effect, and the mechanical strength of riverbank soil reduced because of the freezing and thawing process, which has great effects on the stability of riverbanks. The simulation results of bank erosion were in agreement with the measured data, which demonstrated that the numerical model could simulate the complex channel evolution processes caused by river bed scour as well as bank erosion. This study could provide technical support for the in-depth study of bank erosion and channel evolution in the SFR.