Provided is a silicon-fluorine composite insulator with a 300KN or 400KN breaking load. The silicon-fluorine composite insulator with the 300KN or 400KN breaking load is composed of a plurality of sections of unit insulators in a connected mode, each section of unit insulator comprises a core rod, a fitting ball socket and a fitting ball head, one end of each core rod is fixedly connected with each fitting ball socket, the other end of each core rod is fixedly connected with each fitting ball head, a plurality of umbrella skirts are arranged on the outer surface of each core rod, the fitting ball head of one section of unit insulator is connected with the fitting ball socket of an adjacent section of unit insulator, and the insulator umbrella skirts arranged on the outer surface of each core rod are made of new materials. The silicon-fluorine composite insulator with the 300KN or 400KN breaking load is convenient to transport, install and construct, can be installed in a combined mode to form the lengths needed by various voltage-class electric power circuits, only damaged sections of unit insulators need to be replaced, maintenance cost is greatly reduced, and the insulator umbrella skirts are made of the invented new materials, and have the advantages of being firm, good in tear resistance, good in tread resistance, good in dirty resistance, good in hydrophobicity, and free of the need of protection and sweeping, ensuring safe reliability of power supply of an electric transmission line, and being used for ultrahigh-voltage electric transmission and transformation lines.