The invention belongs to the field of waterproof sealing caps for sealing cable pipe orifices, and specifically relates to a thermal-shrinkage waterproof sealing cap for a high-voltage cable. The sealing cap is low in dependence on the diameter of the cable and the diameter of a casing pipe, and can achieve the better sealing of guide cables and casing pipes in various sizes. The sealing cap employs an insulating material, and a fire retardant is added for preparation, so the waterproof performance is excellent. The sealing cape is suitable for the protection and sealing of various types of cable pipe orifices, such as a cable protection tube and a cable incoming and outgoing mouths of a transformer substation. The sealing cab can achieve the waterproof, fireproof and insulating functionsat the same time, facilitates the early construction operation and the later maintenance management, and no metal part is exposed outside. The sealing cap is good in aging resistance, insulating performance, waterproof and fireproof performances, is good in corrosion resistance, and is good in application prospect.