The built friction torque model is based on. The relationship of the negative axial internal clearance and friction torque of four contactpoint slewing ball bearing was analyzed, and the theoretical analysis were validated through test. The study results show that with the decreased of the negative axial internal clearance of the bearing, the friction torque is increased, and the amplitude is become larger. The equation of the relationship between negative axial internal clearance and friction torque is regressed, and the problem is resolved which is hard to measure the bearing internal clearance in practice.