The invention discloses a welding jig for vacuum brazing between a metal plate and a folded metal sheet. The welding jig comprises a base plate, pressing plate limiting blocks, pressing plate positioning blocks and pressing plates, wherein the two pressing plate limiting blocks are arranged on the two sides of the upper surface of the base plate respectively, a space used for containing the metal plate is formed between the two pressing plate limiting blocks, and the folded metal sheet is placed on the upper surface of the metal plate; each pressing plate is arranged between every two adjacent fins of the folded metal sheet in an inserted manner, the bottom surface of each pressing plate abuts against the upper surface of the connected parts of the bottoms of the two corresponding fins in a pressing manner, the length of each pressing plate is larger than that of the folded metal sheet, the two ends of each pressing plate both protrude out of the two sides of the folded metal plate, and the bottom surface of each pressing plate abuts against the upper surfaces of the pressing plate limiting blocks; and the two pressing plate positioning blocks are arranged above the two pressing plate limiting blocks respectively, and are connected with the two pressing plate limiting blocks through locking bolts respectively, so that the two ends of each pressing plate are tightly pressed between the pressing plate positioning blocks and the pressing plate limiting blocks. With the welding jig for vacuum brazing between the metal plate and the folded metal sheet, the welding quality of vacuum brazing between the folded metal sheet and the metal plate can be improved, and the folded metal sheet is prevented from deforming.