Abstract: Taking axial permanent magnet asynchronous speed-regulation magnetic coupler as research object, a mathematical model of output speed and air gap of speed-regulation magnetic coupler was built based on magnetic circuit method, characteristics of the air gap of magnetic coupler were analyzed, relation between the air gap and output speed of the magnetic coupler under condition of constant load was studied, and variation law of corresponding output speed with different air gaps of the magnetic coupler was obtained: with increasing of the air gap between copper disc and permanent magnet disc, output speed of the magnetic coupler decreases; when the air gap increases linearly from 2.5 mm to 12.5 mm, the output speed decreases gradually from 773 r/min to 723 r/min; when the load torque keeps constant, with increasing of the air gap, power loss increases gradually, and when the air gap increases linearly from 2.5 mm to 12.5 mm, the experimental power loss gradually increases from 565 W to 1 613 W. In actual operation, power loss can be reduced by reducing the air gap properly. The results of the research have a certain guiding significance for the output speed control of the speed-regulation magnetic coupler under condition of constant load.