The invention relates to a center frame of a horizontal lathe. The center frame comprises an upper frame body (2), a lower frame body (1), a fixing bolt (6) for connecting the two bodies, a pressing plate bolt (9) and a pressing plate (10), wherein the upper frame body (2) and the lower frame body (1) are connected by the fixing bolt (6), the lower frame body (1) is a U-shaped frame, an equilateral triangle is formed by taking a center of an inscribed circle of the U-shaped frame as a center, and the corresponding three vertices are respectively provided with frame regulating mechanisms, which is characterized in that the frame regulating mechanism is composed of a slide bushing (3), a slider (13), a frame claw (4), a regulating lead screw (5), a regulating lead screw handle (14), a baffle ring (15), a frame claw lock bolt (7) and a slide bushing lock bolt (8). The center frame has the advantages of reasonable structure, long service life, safety and reliability, capability of processing long and large workpieces, large processing space, convenient use and adjustment, and the like.