The invention discloses a clamp of a pipe hoop-weld welding platform. The clamp comprises a working table. A first stand column and a second stand column are movably connected to the two ends of the working table respectively and can be stretched out or drawn back, a first rotating shaft is perpendicularly arranged at the top end of the first stand column and provided with an overturning base, and a second rotating shaft is perpendicularly arranged at the top end of the second stand column and can be stretched out or drawn back. Compared with the prior art, the clamp has the advantages that as the first stand column, the second stand column, the first rotating shaft, the second rotating shaft, supporting rods, distance sensors and pressure sensors are matched, two to-be-welded steel pipes can be well positioned and rotated, and the welding work efficiency and the welding quality can be improved.