Abstract: In view of the core-pulling problem of the inner hole in the narrow space inside the plastic part, the method of combining the insert with the slanting top was put forward. Taking the plastic shell as an example, the narrow cylinder is first divided into inserts from the core to reduce the processing difficulty of the core, and the lifter is used to shape the side holes in the cylinder, aiming at the interference between the lifter and the plastic part when pulling the core outwards, the core-pulling direction is adjusted to be in the radial direction of the cylinder, and then the interference problem of the slanting top mechanism in the narrow space is solved by embedding the slanting top mechanism on the insert.