A method for controlling an auxiliary step rotated in association with a door opening angle of a vehicle may include a start step of sensing the door opening angle of a door of the vehicle, a first determination step of determining whether the sensed door opening angle is zero, a second determination step of determining whether the sensed door opening angle is less than a preset reference angle, when the sensed door opening angle is not zero, and a first control step of rotating the auxiliary step by the sensed door opening angle, when the sensed door opening angle is less than the reference angle.