In view of the differences between the external insulation level and air gap clearance in practical application at high altitude areas in Tibet and those in plain areas in China, a new method, which combines the actual environment with theoretical formula, has thus been proposed, based on the graphical curves obtained from field experiments, so as to gain high altitude design experience. Combined with the revised formula in the design specification, the revised conclusion is to be obtained subsequently. The results show that the creep ratio distance in engineering application can be obtained by modifying the formula of the relationship between the creep ratio distance and the field pollution degree; a calculation can be achieved of the actual amount of the number of insulator pieces in engineering; the external insulation level and air gap clearance can be obtained by combining experimental graphics and correction formula.