The invention discloses a welding and positioning tool for lower cross beams of front passenger doors of passenger cars. The tool comprises a first positioning plate and a second positioning plate, wherein the first positioning plate and the second positioning plate are connected through a supporting tube; one circumferential side surface of the first positioning plate is an arc-shaped surface; one end of the arc-shaped surface is connected with a first plane; the other end of the arc-shaped surface is connected with a second plane. With the adoption of the manner that the positioning plate matched with a car body and the positioning plate matched with a mounted cross beam are adopted for positioning and mounting, the tool is convenient in positioning, high in mounting efficiency and good in precision; the problem of difficulty in matching welding of the lower cross beams of passenger doors in the passenger car manufacturing industry is solved, the labor is liberated, so that the production efficiency is improved, the labor time is shortened, mounting of the passenger doors in the next procedure is facilitated, and the human resource cost is saved.