The invention relates to a gantry type programmable control girth welding machine, which comprises an automatic control system, a transmission system, a jacking mechanism and a welding gun movement control mechanism, wherein the welding gun movement control mechanism comprises a transverse displacement device, a longitudinal lifting device and a swinging device. In the transmission system, a transmission shaft is provided with a spline and a spline gear, so a main shaft and the transmission system are engaged or disengaged, to manually rotate the welding piece without load. In the working piece jacking mechanism, the welding piece is subjected to flexible compression by an air cylinder pushing jacking needle, to realize the anti-loosening purpose. In the longitudinal lifting device, a stepping motor drives a screw rod to rotate, so the welding gun is lifted to the proper place. In the swinging device, the stepping motor drives a swinging screw rod to rotate forward and reversely, so the reciprocating swinging of the welding gun head is realized, and the technical defects in the existing gantry type programmable control girth welding machine are solved. The welding machine has the advantages that the automation degree is high, the welding quality is high, the operation is convenient, the safety and the reliability are realized, and the like.