Tooth root cracks change the meshing stiffness excitation of gears, increasing vibration and noise in wind turbine gearboxes. Current literature lacks focus on the slicing coupling effect of cracked gears, leading to incomplete accuracy in solving time-varying mesh stiffness (TVMS) under cracked conditions. In this work, a dynamic model of the wind turbine gear-bearing coupling system that considers tooth root cracks and the slicing coupling effect is proposed and verified. Results show that the TVMS modification algorithm, considering slicing coupling effects, can better depicts the dynamic change in gear meshing stiffness under crack failure. Gear crack excitation may alter the dynamic contact load amplitude of bearing rolling elements, reducing the load-bearing area. When cracked teeth mesh, decreased mesh stiffness results in larger amplitude periodic shock responses in system vibration displacement and a sideband phenomenon near the mesh frequency. Neglecting the slicing coupling effect or simplifying the bearing to a linear support stiffness matrix risks underestimating the influence of gear crack depth on the vibration displacement of the gear-bearing coupling system.