As an important component of power equipment in rail transit, the vibration characteristics of subway gearboxes have a significant impact on the safe operation of the subway. Due to the harsh working environment of high-speed overload, frequent start and stop, and speed variations, the gears and bearings in the subway gearboxes are prone to failure. This study establishes a gear-bearing coupling model of the subway gearbox considering the bearing defects using the lumped parameter method. The effect of the bearing defects on the vibration characteristics of the system are analyzed. The results show that the vibration signals of a subway gearbox transmission system are modulated when the inner raceway of the bearing is faulty. Considering gear-bearing coupling results in a larger shock amplitude of the system than considering a single bearing when rollers pass through the defect region, but the shock frequency in both cases is the defect frequency of the bearing.