The altitude correction and electric field strength control of corona effect for AC transmission lines are the key factors for selection and configuration. At present

the research on corona characteristics of UHV power fittings over 3 km altitude is rarely available in the literature

and the regularity is not perfect. Therefore

the corona characteristics of different fittings are simulated under different altitude conditions by using environmental climate chamber

and a segmented altitude correction calculation method is proposed which is suitable for corona tests of grading and shielding rings. The field strength control value of high altitudes is obtained by combining corona tests and finite element simulations. According to the design requirements of 3~5 km altitude

the selection schemes of fittings for suspension and tension insulator string are required by the modeling and simulation software. According to the simulation

the recommended schemes are verified by visible corona tests at the altitude of 23 m and 4 300 m

and the corona extinction voltages are higher than the specified voltage and have a certain margin. The tests can meet the requirements of high-altitude UHV transmission lines. The research results have been applied to the design of Sichuan - Chongqing high altitude UHV transmission project of china.