The present invention provides a method and an apparatus for dynamically controlling the luminance of a tail light of a vehicle tail lamp in response to a change in the difference of speed between a vehicle and a vehicle therebehind, and for preventing a collision between the traveling vehicles. In addition, the apparatus comprises: a tail light operating unit, which slowly or rapidly becomes brighter up to a predetermined brightness as the speed difference between the vehicle and the vehicle behind gradually becomes larger, and slowly or rapidly becomes darker down to a predetermined brightness as the speed difference between the vehicle and the vehicle behind gradually becomes smaller; a speed sensing unit for measuring the speed of the vehicle; a rear speed sensing unit for measuring the speed of the vehicle therebehind; and a control unit for automatically adjusting the luminance of the tail light by controlling the tail light operating unit when the vehicle therebehind is traveling faster than the vehicle.