A control system of a milling machine is disclosed. The milling machine has an overarm, a spindle connected to a cutter, a spindle motor, and an X-axis motor, a Y-axis motor and a Z-axis motor. The control system includes a vibration sensor for detecting a vibration level of the spindle. The control system also includes a central control unit configured to adjust a rotation speed of at least one of the X-axis motor, the Y-axis motor, and the Z-axis motor to bring a load current of at least one of the motors to be within a corresponding current range, and configured to adjust a rotation speed of the spindle motor to bring the vibration level to be within a vibration range.