The 20 t resistance and chopper speed-regulating motor vehicles used in Dahongshan Iron Mine have many problems such as high failure rate of electrical control system,large maintenance,and high maintenance cost,which is difficult to meet production requirements.In order to solve the problems in the process of using the electric motor car,through the research on the speed control system of the electric motor,the variable speed direct torque control mode is s.e.l.e.c.ted to upgrade the speed control mode of the electric motor vehicle.It has been proved by practical application that the frequency conversion speed regulation not only effectively solves the above problems,but also has good speed regulation performance,reliable operation,easy maintenance and remarkable energy saving effect.The necessity and widly application prospect of applying the direct torque control mode variable frequency speed regulation technology to transform the DC motor shaft motor is obtained.