Abstract: By use of the equivalent magnetic charge method, the formula for calculating the maximum torque of the permanent magnet overload separation device was established. The relation between the separation torque of the device and dimensions of the device were studied. Studies show that as the axial dimension of the magnet increases, the separation torque increases linearly. Increasing the width of the magnet will cause an increase in the separation torque, and the width of the magnet has different influences on the separation torque in different ranges. In terms of using the theoretical maximum width of magnetic blocks corresponding to its number in the calculation, it could be found that with the increase of the number of magnetic blocks, the separation torque first increases and then gradually decreases. With the width of air gap and the radius of air gap increase, the separation torque will generally decrease. According to the theoretical research, a prototype of permanent magnet overload separation device was designed, developed and tested.