Hysteresis Clutch can produce torque according to electromagnetic theory,The exciting current and the output torque becomes the proportional relationship basically. It can transmit torque but not because of slip frequency and has many advantages: such as simple structure, no pollution,no noise,no impact on the vibration,energy saving etc. Hysteresis clutch that is a multipurpose the superior performance of automatic control components can be widely used in many tension control field.