The invention discloses a clamp for annular welding of a workpiece. The clamp comprises an L-type workbench. A feed channel and a discharge channel are formed in the workbench, and a rotating table ishinged to the position, at the joint of the feed channel and the discharge channel, on the workbench. A material channel communicating with the feed channel is formed in the upper end surface of therotating table. Clamping pieces are arranged on the positions, at the two sides of the material channel, of the rotating table and comprise clamping plates and hinge shafts. The clamping plates comprise plate bodies and clamping bodies. Annular shaft sleeves are formed in the plate bodies. The hinge shafts are connected in the shaft sleeves in an inserting mode. Arc grooves are formed in the outerwalls of the hinge shafts. Insertion blocks are connected in the arc grooves in an inserting mode and are formed on the inner walls of the shaft sleeves. Arc-shaped compression springs are arranged in the arc grooves in an inserting mode, and the two ends of the compression spring abut against the inner walls of the arc grooves and the insertion blocks correspondingly. Annular grooves are formedin the rotating table, and first insertion blocks and second insertion blocks are connected in the annular grooves in an inserting mode and are formed at the bottoms of the plate bodies. By means of the clamp, the round shell-shaped workpiece can be automatically and conveniently clamped after automatic feeding, and can be automatically discharged after welding is finished.