The invention discloses a laser ground projection type commercial car body length initiative visual detection system which aims at solving the problems that length direction image collection and initiative visual measurement of a whole large size commercial car can not be achieved. The system comprises a line projector assembly body base (1), a line projector seat (2), a line projector clamp (3), a camera seat (4), a camera (5), a line projector (6) and a drum-type braking test table (7). According to the laser ground projection type commercial car body length initiative visual detection system, a non-contact automatic measuring system capable of automatically collecting car body laser projecting rays and measuring the length of a car body through initiative machine visual sense.