As more and more converter stations are constructed at high altitude, how to reasonably select the minimum air spacing of converter station substation equipment has become an important issue for DC power transmission at high altitude. In order to study the influence of air environment on switching impulse discharge characteristics of air gap at high altitude, this paper conducts switching impulse discharge tests on 1m rod-plate air gap under different air pressure, temperature and humidity conditions, investigates switching impulse discharge characteristics of rod-plate air gap at high altitude, and compares and analyses differences in correction results of various discharge voltage correction methods. Studies have shown that air pressure as well as temperature and humidity have an effect on air gap discharge voltage. Meanwhile, based on different atmospheric parameters, correction formulas are obtained for 1m rod-plate air gap discharge voltage, and the elevation correction coefficients of 1m rod-plate air gap at each altitude was obtained. The results of the study provide a reference for external insulation of equipment and its insulation fit in converter stations at high altitude.