The invention discloses a clamping fixture for processing the inner wall of an engaging lug on a weld yoke based on a processing center. The clamping fixture comprises a first support plate, connection plates, a support table, a second support plate, first pressing rod, first pressing plates, second pressing rods, a second pressing plate, a positioning round boss and ejector rods, wherein the two connection plates are connected with the first support plate; the support table is connected with the first support plate; the second support plate is fixed on the support table; the positioning round boss is fixed on the second support plate; multiple ejector rods are uniformly distributed on the second support plate; two first pressing rods are vertically connected with the left and right sides of the second support plate respectively; four second pressing rods are connected with the second support plate; the first pressing plate and the second pressing plate are rotatably connected with the first pressing plates and the second pressing rods respectively; the first pressing plate is pressed in a limiting groove; and the second pressing plate is pressed on the end surface while a cross-axle connection part is tightly placed against the ejector rods. The clamping fixture disclosed by the invention has the advantages of few clamping times, high working efficiency, balanced fixture stress and good clamping effect.