The utility model provides a milling jig which solves the technical problems that an existing clamping mode is unreliable and greatly depends on manual experience in the machining process of an existing semicircular inner hole part. Base seat, upper panel is arranged on the base, a swing arm seat is arranged on the upper panel; a swing arm opening groove is formed in the swing arm seat; a swing arm is arranged in the swing arm opening groove; the swing arm is connected with the swing arm seat through an upper end rotating pin; a cushion block and a stop block are arranged at the upper end of the upper panel; a screw seat is arranged at the lower end of the upper panel; a sliding sleeve is arranged in the screw rod seat; a locking nut is arranged on the end face of the sliding sleeve, threads are arranged on an inner hole of the sliding sleeve, a flat key groove is formed in the outer circle of the sliding sleeve, a flat key sliding groove is formed in an inner hole of the screw seat, aguiding flat key is arranged between the sliding sleeve and the screw seat, and a driving screw and a connecting screw are arranged in the screw seat. The clamp can be widely applied to clamping of various workpieces.