The invention discloses a light-weight adjustment line vehicle door assembling locating mechanism convenient to use. The mechanism comprises a first locating fixture and a second locating fixture. Thefirst locating fixture comprises first locating pins, screws and nuts, the first locating fixture is attached to a side wall through vehicle door hinges to achieve Y-direction location, and X-direction location and Z-direction location of a vehicle door and the side wall are achieved through the first locating pins installed on the vehicle door hinges. The second locating fixture comprises a locating base body, magnet holes, a second locating hole and a third locating hole are formed in the locating base body, magnets are embedded in the magnet holes, the locating base body is attracted to aside wall lock catch to achieve X-direction location, a second locating pin is arranged in the second locating hole, a third locating pin is arranged in the third locating hole, and Y-direction location and Z-direction location of the second locating fixture and a vehicle door U-shaped groove are achieved through the second locating pin and the third locating pin. The first locating fixture and the second locating fixture are adopted, locating stability is high, operation time is short, production efficiency is high, the weight is low, and the labor intensity of workers can be reduced.