Abstract: To avoid the rub and damage to the sealed inner pack (hereinafter referred to as inner pack) and the neck scratches of shoulder box during the box filling process, a movable guide mandrel was designed for a YB424 hard packer. The movable guide mandrel is mainly composed of a drive mechanism, a mandrel framework, and four movable guide blades made of ZGMn25 manganese steel with a movement angle of 19.47° forming a flexible funnel. The drive mechanism vertically drives the movable guide mandrel through a disc cam and a four-bar linkage. Along with the movable guide mandrel, the inner pack moves downwards into the shoulder box, the four movable guide blades changed from an inclined state to a vertical state under the action of springs to correct the position of the shoulder box and precisely guide the inner pack into the shoulder box. The YB424 hard packer was tested with "Yunyan (Demi-slim Dachongjiu)" cigarettes. The results showed that compared with the fixed mandrel, the movable guide mandrel effectively prevented the inner packs from blocking the packer, and reduced the probability of the defective inner packet during the filling process from 0.59% to 0. This technology provides support for improving the production efficiency and packing quality of cigarette shoulder boxes with sealed inner packs.