Abstract: The design of anti-corona fittings is the key to the prevention and control of corona and electromagnetic environment at the UHV substations, especially in high-altitude areas where corona prevention is particularly important. In this article, by using the finite element simulation combined with the experimental, the altitude correction index formulas, the linear formulas, and the metal surface field strength control values that meet the engineering requirements are proposed. The electric field distribution on the surface of the wire connection fittings at the high-altitude UHV substations is calculated, and the structural optimization schemes for each of the wire connection fittings are provided, which are verified through the high-altitude corona tests. The results show that the correction coefficient for the 4000m altitude calculated in this proposed method is 1.51, which is 1.9% different from the recommended value of Q/GDW 551-2010. The differential control should be carried out on the surface field strength of the wire connection fittings at the high-altitude UHV substations: the upper layer fittings should not exceed 1.32kV/mm thick with the local not thicker than 1.52kV/mm; the lower level hardware should not exceed 0.99kV/mm thick with the local not thicker than 1.14kV/mm. When adopting the recommended scheme in this article, the corona extinction voltage of all the wire connection fittings is higher than 698.5kV but maintains a certain safety margin, which is able to meet the requirements for the use at the 4000m high altitude 1000kV substations. The research results of this article will provide a basis for the design of the anti-corona fittings for the 1000kV substations at the ultra-high-altitude areas in China, assisting in the construction of a green and environmentally friendly new energy system in China.