The utility model relates to an expanding device for 110kV cable main insulators. The expanding device includes a body of the expanding device; the body is provided with a stressed connection plate through a rotating shaft; a screw hole is formed at the upper end of the body; a pressing screw is mounted in the screw hole; and an expanding head is installed at the low ends of the body and the stressed connection plate. The expanding device for the 110kV cable main insulators of the utility model is used in cooperation with an electric molding cutter for the 110kV cable main insulation, so that separation work of the cable main insulation can be converted into simple, rapid and labor-saving and efficient semi-automatic construction from traditional manual rotary cutting.