The present invention discloses a bicycle direction light control system which may be installed on a bicycle and a head fitting. The system includes a sensing module and a direction light module. The sensing module can be installed on the head fitting for sensing the movement speed, turning angle and turning direction of the user's head. The direction light module is installed on the bicycle and faces towards the rear side of the bicycle. During the moving of the bicycle, when the sensing module senses that the turning angle of the user's head changes to a preset angular range within a sensing period, the direction light module turns on a corresponding indicator light according to the turning direction of the user's head.