The invention relates to a universal clamp for numerical control machining on a nozzle segmental arc of a steam turbine. The problems of the current clamp for machining the nozzle segmental arc of the steam turbine that the universality is poor, the occupation space is large and the production cost is increased are solved. A rectangular plate, a large-diameter fan-shaped plate and a small-diameter fan-shaped plate are integrated; three rectangular slide grooves are formed in the surface of the rectangular plate along the transverse direction of a clamp plate; the long side walls of the three rectangular slide grooves are arranged in the manner of being parallel to the longitudinal central line of the clamp plate; the center of the middle rectangular slide groove and the middle point of the longitudinal central line of the clamp plate are overlapped; two first fixing pins are fixedly connected with the small-diameter fan-shaped plate; two second fixing pins are symmetrically arranged in the manner of being relative to the longitudinal central line of the clamp plate and are fixedly connected with the large-diameter fan-shaped plate; and the two first fixing pins and the two second fixing pins are symmetrically arranged in the manner of being relative to the longitudinal central line of the clamp plate. The universal clamp is used for clamping and fixing when the nozzle segmental arc of the steam turbine is machined.