With the development of power industries, in recent years, more and more switchgears used in high altitude were needed in China market. At the region of higher altitude, due to the lower air density, the insulation strength of air sharply decreases, so external insulation design of electrical equipment used in high altitude regions is a critical factor.

In this paper, a new post insulator applied in 3500m altitude was developed, design test results shows that this new insulator did not satisfy with requirements of high altitude application. For improving the product performance, electrical field simulations were implemented to optimize the design of new insulator. Based on these simulation results, we can find two different improvement methods:1) modify the shed structures of new post insulator, 2) change the design of high voltage inserts involved in post insulator. Verification test results can prove that two improvement methods can effectively increase the insulation capacity of insulator.