Abstract: Taking a magnetic coupling as the research object, this paper proposes a method of grooving on the magnet disk to increase the maximum starting torque of magnetic coupling, and theoretically studies the cogging torque caused by this method. The virtual displacement method is analyzed based on the analytic formula of cogging torque, we find the key factors affecting the cogging torque, and simulate each kind of optimization method of calculation results through three-dimensional finite element analysis software, the results prove that this method is feasible.