In high-altitude areas, as the elevation increases, the air density gradually decreases, leading to a corresponding reduction in the insulation level of the same air gap. It can be seen that designing air gaps appropriately is crucial for the safety and economic operation of power grids. Correcting air gaps at high altitudes has significant practical implications. However, the current research system in China regarding external insulation and air gap corrections for substations at high altitudes is still not mature. This paper is based on the true model test data under standard meteorological conditions provided by the GB/T 24842 standard for theoretical analysis. Using the altitude correction methods from two standards, IEC 60071-2:2018 (m coefficient method) and IEC 60060-1:2010 (g parameter method), the study performed altitude corrections for the power frequency, lightning impulse, and standard operating impulse of typical gaps in AC substations. Discharge voltages were obtained for altitudes ranging from 2000 m to 5000 m, and several important discharge characteristic parameters were acquired. By comparing the correction results of the two methods, this study provides insights for conducting true model tests of gap discharges in ultra-high voltage AC substations at high altitudes.