The invention discloses a special cement sleeve online machining device and relates to the field of cement equipment maintenance. The special cement sleeve online machining device comprises a lathe bed and a grinding mechanism transversely sliding along the lathe bed. A large supporting plate sliding in the longitudinal direction is arranged on the surface of the lathe bed, and a vertical plate perpendicular to the sliding direction of the large supporting plate is fixed to one end of the upper surface of the large supporting plate; the grinding mechanism comprises a grinding wheel and a driving motor, the grinding wheel is connected with the driving motor through a transmission belt, the grinding mechanism is connected with a small supporting plate through a slideway, a screw rod driven by a hand wheel is fixed to the small supporting plate, and a nut matched with the screw rod is fixed to the grinding mechanism; the small supporting plate is fixed to the large supporting plate or the vertical plate through bolts; a rack is fixed to the lathe bed in the longitudinal direction of the lathe bed, a motor is fixed to the large supporting plate, and a gear a meshed with the rack is fixed to an output shaft of the motor; the lathe bed is further fixedly provided with a manual adjustment mechanism playing a fine adjustment role in sliding of the large supporting plate. Online machining of cement sleeves can be achieved without disassembling the cement sleeves, disassembling cost is saved, and the application range is wider because of horizontal and vertical conversion.