Abstract: It is extremely important to determine the external insulation level of Ultra High Voltage（UHV） substation in high altitude area to ensure the reliability and economy of power system. This paper reviews the existing methods of external insulation design for high-altitude areas, takes Ganzi UHV substation as an example to calculate its external insulation level and compares the results with the experimental results. The comparison results indicate that the existing calculation results of ultra-high voltage external insulation coordination are too conservative. In addition, when existing methods are applied to high-altitude areas, there are still problems such as lack of theoretical basis for selecting gap factor values, the schematic range of altitude correction curve and insulation discharge curve is insufficient, and he standard insulation level sequence is too short, thus, this paper proposes measures such as conducting insulation discharge tests at different altitudes, improving discharge functions and curves for various structural gaps, and increasing standard withstand voltage sequences, which indicates the direction for the future research work.