In order to find the regularity and mechanism of armature current′s abnormal fluctuations in main drive system during rolling process with steady speed and acceleration, the direct side armature current of direct current speed controller is tested with Hall sensor. Detection data are observed by the digital oscilloscope and extracted, then the spectrum is analyzed. By analyzing the test results and other potential external disturbance, it is found that this situation is caused by rolling torsional vibration as well as the external load disturbance. After theory analysis and experimental approvment, the torsional vibration and abnormal current fluctuation can be supressed through adjustment in filtering time constant of speed loop and proportion coefficient in main drive control system, which makes the current fluctuations within ±3％.