The invention relates to an oversized wedge block inner tube core with a built-in oil cylinder. The oversized wedge block inner tube core with the built-in oil cylinder comprises a front travelling mechanism, a back travelling mechanism, a rising mechanism, a translation mechanism and a transition and locating combining mechanism. The oversized wedge block inner tube core with the built-in oil cylinder is characterized in that the rising mechanism comprises two upper rising plates, two lower rising plates, a plurality of upper supporting racks, a plurality of lower supporting racks, a plurality of upper rising slide blocks, a plurality of lower rising slide blocks and a plurality of rising recovery plates; the translation mechanism comprises two movable plates, a connecting plate, a limiting plate, an oil cylinder, a connecting shaft head, an oil cylinder head, limiting bases, limiting gaskets, a plurality of pairs of movable slide blocks and four recovery plates; and the transition and locating combining mechanism is composed of two translation and locating mechanisms which are symmetrically arranged above and below the oil cylinder base, wherein each of the translation and locating mechanisms is composed of two locating bases which are fixed on the two upper rising plates or the two lower rising plates, a supporting shaft which is hinged between the two locating bases and a guide shaft which is perpendicular to the supporting shaft and is hinged to the middle part of the supporting shaft. The oversized wedge block inner tube core with the built-in oil cylinder prevents a steel pipe from being out-of-round and wrinkling when a pipe bender is used for bending a pipe, has enough structural strength and anti-bending deformation capacity, and is long in service life and convenient to maintain.