The invention discloses a mounting auxiliary tooling of a car lamp rear cover. The mounting auxiliary tooling comprises a pressure bar, a pressure bar head and a handle, wherein the handle is arranged at one end of the pressure bar; the pressure bar head is arranged at the other end of the pressure bar; and a pressure groove matched with the outer end surface of the rear cover is formed in the end surface of the pressure bar head. Through the adoption of the mounting auxiliary tooling, the rear cover can be quickly mounted in place, and is compacted and mounted through the pressure bar, so that the labor intensity is low, and the production efficiency is high; besides, the pressure bar head is matched with the outer end of the rear cover, so that the stress is uniform, the mounting uniformity of the product is good, and the mounting quality of the car lamp rear cover can be greatly improved.