The invention relates to a pneumatic ejecting mechanism of a welding jig. The pneumatic ejecting mechanism is characterized by comprising a cylinder, a mechanical valve, an air tube, a stand, an ejector plate, a first ejector rod and a second ejector rod, wherein the stand is fixedly arranged on the welding jig, the cylinder is fixedly arranged on the stand, an air inlet and an air outlet of the cylinder are respectively connected with the mechanical valve by the air tube, a piston rod of the cylinder is controlled to stretch out and draw back by the mechanical valve, the piston rod end of the cylinder is connected with the ejector plate, the first ejector rod and the second ejector rod are arranged on the ejector plate, allowance holes through which the first ejector rod and the second ejector rod can penetrate are formed in a bottom plate of the welding jig, and the first ejector rod and the second ejector rod can freely move on the corresponding allowance holes. The pneumatic ejecting mechanism is simple, compact and reasonable in structure, welded parts in the welding jig can be ejected out in a pneumatic manner so as to be taken conveniently, the problem of difficulty in taking the welded parts can be eliminated, the time for taking the parts can be greatly shortened, and the welding work efficiency can be improved so as to win the benefits for enterprises.