<p>In nuclear power plants, vertical rotor-bearing systems of circulating seawater pump units employ gear couplings to link motors and gearboxes. Prolonged misalignment and vibration loads in such systems risk operational safety by inducing bearing defects. Existing dynamic models for gear-coupled rotors often overlook the coupled mechanisms between misalignment and bearing defects, particularly how misalignment-induced loads influence bearing contact forces. To address this gap, this study proposes a novel dynamic model integrating gear coupling misalignment with bearing defect interactions. By formulating time-varying contact widths for meshing teeth under compound misalignment, the model enhances meshing force calculation accuracy in misalignment conditions. A coupled bearing contact force model, linking misalignment loads to defect-driven raceway deformations, clarifies fault evolution dynamics under combined excitations. The model further enables vibration response prediction across speed and misalignment variations, surpassing conventional methods in characterizing coupled fault features. CRF simulator experiments validate its superior accuracy in identifying bearing defect frequencies and their modulations under misalignment conditions, outperforming the existing models. This work enriches diagnostic basis for compound faults in the gear-coupled rotor system.</p>