An intermediate roller assembly for a straightening machine for medium and thick plates is used for a sixfold type medium and thick plate straightening machine roller box in steel and nonferrous industries. An intermediate roller is provided with a spiral groove, two ends of the intermediate roller are provided with a thrust cylindrical roller bearing and a needle bearing, an end cover is arranged on the end face of the intermediate roller, the needle bearing and the thrust cylindrical roller bearing are arranged in a bearing casing, and the thrust cylindrical roller bearing is located axially. A lip opening of a sealing ring is attached to a sealing loop, the sealing ring is arranged on the bearing casing, an inner hole of the sealing loop is provided with an annular groove, a dustproof cover fastens the sealing loop on the intermediate roller through a screw, an inner conical face of the dustproof cover enables metal foreign matters to be thrown out in a centrifugal mode or fall freely, a top cover is connected with the bearing casing through a screw, the outer end face of the top cover is a spherical face, and the bearing casing is located axially through the end cover. The intermediate roller assembly has good sealing performance, can effectively prevent the foreign matters from entering the bearings, is high in bearing capacity, can reduce fault hidden danger and avoids tremendous economical loss caused by unexpected halt and overhauling.