The utility model relates to a composite post insulator used in the transmission and transformation of power industry, which consists of a winding pipe, a mandrel, an end part connecting piece, an umbrella body and a sealing ring; wherein, the surroundings of the mandrel is wound with the winding pipe which is wound and solidified by the glass fiber yarn soaked with epoxy resin glue; the external of the winding pipe is bonded with an umbrella body which is a one-off integral injection molded structure using heat-curable silicone rubber as the material; both ends of the winding pipe are respectively bonded with the end part connecting piece with a strengthening groove; the sealing ring is arranged between the external surface of the winding pipe and the end part connecting piece; as the sealing ring is arranged between the winding pipe and the end part connecting piece, the sealing effect is increased and the electric corrosion caused by the entrance of aqueous vapor to the interface is reduced; as the internal diameter of the end part connecting piece is provided with a plurality of annular grooves and axial grooves, the connection between the winding pipe and the end part connecting piece is more reliable, the connecting strength is enhanced and the wind resistance capacity in strong storms is increased.