Abstract: The paper analyzed the theory of improving start performance of coiling asynchronous motor and proposed a control scheme of improving start performance of asynchronous motor, namely parallelling chopper and start resistor of rotor rectifier circuit, and continuously changing duty cycle of the chopper to make start resistor of motor maintain a constant value with increase of rotate speed of motor in starting process, so as to ensure little start current when motor torque is large, shorten start time, speed up start process, and achieve purpose of improving start performance. It discussed implementation method of the control scheme and gave calculation formula and an example of start resistor parameter. The calculation principle and example demonstrated feasibility of the control scheme.