The invention discloses a side marker lamp control method which is used for controlling a side marker lamp of an overlength vehicle. The side marker lamp control method comprises the following steps: 1) detecting whether the switch of at least one of the danger signal lamp and steering lamp of the overlength vehicle is turned off, if yes, controlling the side marker lamp to be in a glittering state, and if not, executing step 2); and 2) detecting whether the switch of at least one of the foglamp and driving lamp of the overlength vehicle is turned off, if yes, controlling the side marker lampto all light, and if not, turning off the side marker lamp. Two states of the side marker lamp ensure that the side marker lamp has the action of warning users on other roads when the overlength vehicle is under various working conditions, thereby improving the warning function of the side marker lamp, reducing the possibility of safety misadventure of people in the middle of a vehicle body or vehicles and improving the safe reliability of the overlength vehicle. The invention also provides a side marker lamp control system and an overlength vehicle adopting the control method and the controlsystem.