The invention relates to a wound roll structure of a reeling machine. The wound roll structure is characterized in that: the rear end of a mainshaft is provided with a dilatation hydraulic cylinder; the center of the dilatation hydraulic cylinder is connected with a mandrel which is inserted into the center of the mainshaft; two ends of the mandrel are provided with a first lining and a second lining respectively; a cross fork is fixed at the front end of the mandrel by a nut; the cross fork is connected with an axial oblique wedge; the mainshaft is provided with a groove; the axial oblique wedge is arranged in the groove; a first radial oblique wedge and a second radial oblique wedge are arranged outside the axial oblique wedge; a fan-shaped plate is arranged outside the first radial oblique wedge; a fixed tong plate is fixed on the fan-shaped plate by a bolt; a movable tong plate is connected to the second radial oblique wedge by the bolt and a second disc spring; and a tong mouth consists of the fixed tong plate and a movable tong plate. The wound roll structure has large dilatation amount and is convenient to detach and roll; the tong mouth is large; the thickness range applicable to a strip material is wide; the magnitude of the clamping force can be automatically adjusted according to the thickness of the strip material; when a wound roll is in a dilatation state, the cross section of the wound roll has a full circle shape; and when the thin strip material is reeled, the strip material cannot generate crease.