The invention discloses a welding fixture of a heavy truck bumper assembly. The welding fixture comprises a work platform; a positioning device is arranged at the same side of the work platform; the positioning device comprises a support, a plurality of limited posts, a regulating device, a plurality of supporting columns, a plurality of positioning pins and fixing devices of the positioning pins; one ends of the supporting columns are fixedly connected with the work platform, and the other ends of the supporting columns are sleeved on the fixing devices; the structure of the support is matched with the external surface structure of the bumper assembly; the distribution positions of the limited posts, the regulating device and the supporting columns on the work platform are matched with corresponding positions of installation holes of the bumper assembly on a bumper; and the distribution positions of the positioning pins on the work platform are accordant with the corresponding positions of a plurality of welding components on the bumper. The welding fixture has the beneficial technical effect of simple structure; the positioning pins can automatically align the welding positions of the welding components on the bumper assembly; and the working efficiency is improved.