The invention discloses a method and device for extruding and shrinking a casing, and belongs to the technical field of casings. The device comprises a rack, and is characterized in that the rack is provided with a first moving support and a second moving support which can move in opposite directions, the first moving support is provided with a first extrusion head, the second moving support is provided with a first plier arm and a second plier arm, the first plier arm and the second plier arm are connected with an opening and closing mechanism, a first split body is arranged on the first plier arm, a first clamping groove is formed in the first split body, a second split body is arranged on the second plier arm, a second clamping groove is formed in the second split body, the second clamping groove can be in butt joint with the first clamping groove to form a clamping hole, and the first split body and the second split body form a second extrusion head; and the second extrusion head and the first extrusion head are distributed oppositely. By means of the device, the two ends of the casing shrinkage pipe can bear extrusion force at the same time to be compacted towards the middle, the compactness of the casing shrinkage pipe can be improved, and disjunction is avoided; and the pipe wall of the casing shrinkage pipe is arched outwards, so that the hole in the casing shrinkage pipe is expanded, and the rod is convenient to separate.