High performance speed closed-loop control is the key to precision servo control system. According to the larger error of speed loop when reversing, an Active Disturbance Rejection Controller (ADRC) is put forward to speed closed-loop for precision servo control system. ADRC can estimate the internal and external disturbances in real time, and it does not depend on the object model. Based on the frequency-domain characteristics of controlled object, linear ADRC was designed, the relationship between the resonant frequency and the object parameter b was found, other parameters tuning method was presented, and all of these provided the basis for experiment parameter debugging. Finally, under the same bandwidth, the ADRC and conventional PI controller are applied in speed closed-loop respectively to make comparative experiments. Actual results show that ADRC can significantly reduce the reversing error and improve the system tracking accuracy when the input signal is 0.5° and 1.0°.