The utility model discloses a caliper used for measuring pipeline ovality. The caliper comprises a clamp body. The clamp body comprises two clamp legs whose end portions are hinged through an articulated shaft. The articulated shaft is provided with a rotation angle sensor used for detecting a relative rotation angle signal of the two clamp legs. The rotation angle sensor is connected to a digital display box used for displaying a corresponding angle value. The digital display box is arranged on one clamp leg. The caliper has the advantages that after position clamping is performed on a pipeline bend pipe or a bend head, the caliper does not need to be removed so as to carry out reading and an angle value can be read directly; the clamp legs of the caliper are fastened at a maximum distance point so that numerical value accuracy can not be influenced because a distance between the two clamp legs is changed. Electronic and mechanical modes are used to measure the angle so that an error is reduced.