Abstract: The momentum wheel is a key device used for orbiting satellite attitude control. Its controlling accuracy is strongly influenced by the cage stability of the ball bearings in momentum wheels. The more stable the cage, the smaller the friction moment of the bearing, and the higher the control accuracy of the momentum wheel. In this study, an ADAMS multi-body dynamic model of ball bearings was built. In this model, the collision and friction were considered, which exist in the components of the ball bearing, that is, the balls, the rings, and the cage. The whirl behavior of the cage of the ball bearing used in the momentum wheel was analyzed under variable working conditions, and the cage stability was quantitatively analyzed. The effects of starting acceleration, axial load, and gravity field on the cage stability were discussed. The results show that an increase in the starting acceleration of the ball bearings can shorten the starting time, and the guiding effect of the guiding face on the cage is enhanced. Moreover, the cage is more stable when the speed of the ball bearing is higher. However, the greater starting acceleration can increase the friction moment of the ball bearing, which can shorten the service life. Under the premise of satisfying the cage stability, a smaller starting acceleration should be used as far as possible to prevent the larger friction moment. An increased axial load causes a strong collision of the cage and balls and increases the cage whirling state. The friction moment of the ball bearing increases when the axial load increases, which can lead to the generation of the wear and heat of bearing. In addition, an increase of the axial load of the ball bearing aggravates the collision of the balls and cage and increases the whirling state of the cage, and this reduces the cage stability. The collision of the cage and ring increases without gravity, causing an increase in the cage whirl.