Abstract: Based on the principle of feedback control, this paper presents that making use of current amplifier and voltage amplifier, as a means of control, can make the controlled object running strictly under the varied distribution characteristics of rotational speed with high accuracy and convenient operation. In addition, the structure of the control system is simple. In analysis, the transfer functions of both input signal/rotational speed and loaded torque/rotational speed are obtained. Moreover, according to the transfer functions mentioned above, the transient of the rotational speed response to input signal and loaded torque is also analysed.