An access point in a geographic routing system and a controlling method thereof are provided. The controlling method of the access point in the geographic routing includes the following steps. A traffic event packet is received by the access point. A back-off timer of the access point is set to be a first back-off time value. The first back-off time value is less than a second back-off time value of any on board unit (OBU) which receives the traffic event packet. The traffic event packet is broadcasted by the access point when the back-off timer is counted down to be zero.