The electromagnetic design of the high speed ratio asynchronous motor, that was, to meet the high speed weak magnetic area torque, but also to overcome the low speed when the magnetic passing through saturation. 1 600 kW asynchronous motor as an example, analysis of the equivalent circuit parameters change characteristics, the low speed torque, efficiency, voltage, current and power factor curve drawing, and the magnetic flux density, magnetic permeability distribution, distribution and temperature rise time loss under different conditions were calculated by the motor type test. The design met the technical requirements.