The invention discloses a sleeve replacement device and an automatic tightening system. The sleeve replacement device comprises a sleeve rack, wherein the sleeve rack is provided with long-strip-shaped storage grooves for storing sleeves; the sleeves and tightening shafts can enter the storage grooves from one end of the storage grooves; clamping blocks are arranged on an inner side wall of the other end of each storage groove; the clamping blocks are used for clamping the periphery of the sleeves and separating the sleeves and the tightening shafts. The sleeve rack is provided with the storage grooves for storing the sleeves and the storage grooves are long-strip-shaped; the width of the storage grooves is adaptive to a size of the stored sleeves; the clamping blocks are arranged at one end of the storage grooves and are used for clamping the periphery of the sleeves; no clamping block is arranged at the other end of the storage grooves so that the sleeves and the tightening shafts can be stored into the storage grooves from the ends; the sleeves are driven by the tightening shafts to slide to one end provided with the clamping blocks; when the clamping blocks clamp the periphery of the sleeves, the tightening shafts are pulled out, so that the tightening shafts and the sleeves can be simply separated; a process of storing the sleeves into the tightening shafts is just opposite to a process of separating the sleeves from the tightening shafts; the process of mounting the sleeves on the tightening shafts or dismounting the sleeves from the tightening shafts can be simply and effectively realized.