According to an alligator clip, an upper clamping piece and a lower clamping piece are hinged to each other through a rotating shaft; the rotating shaft is equipped with a rotation spring; two ends of the rotation spring are respectively applied to the upper clamping piece and the lower clamping piece; the opposite sides of the upper clamping piece and the lower clamping piece are respectively provided with teeth which are mutually engaged; and the front ends of the upper clamping piece and the lower clamping piece are respectively provided with semicircular apertures, and the two semicircular apertures form an integral circular hole. When the alligator clip is used for transient circuit connection, the front end integral circular hole is sleeved on the nut of a detected bolt, reliable electric connection is formed, jumper-wire and short-circuit problems happening when a screw rod is clamped along the axial direction of the prior alligator clip are solved, and the alligator clip is characterized in that the structure is simple, usage is convenient, and the alligator clip is safe and reliable.