The paper focuses on the problem of high risk of pollution flashover in transmission lines under extremely heavy salt concentration in the desert area of northwest China. A study was conducted on the pollution flashover characteristics of 420kN standard and 3-sheds ceramic insulators. Two types of insulators with pollution flashover characteristics were obtained under extremely heavy salt deposit density (SDD) of 0.25 mg/cm2, 0.35 mg/cm2, and 0.5 mg/cm2. The results show that there is a power function relationship between the 50% flashover voltage (that isU50%) of the insulator and SDD. Compared with 0.25 mg/cm2, U50% at 0.5 mg/cm2 decreases by a maximum of 22.5%. Under the same SDD, the U50% of a standard ordinary insulator is 13.9%–28.7% lower than the U50% of 3-sheds-alternate insulator. Under extremely heavy salt density conditions. Under extremely heavy salt density, when the SDD is less than 0.5 mg/cm2, the flashover voltage per unit creepage distance is also lower than that of the alternate insulator. Considering that the 3-sheds-alternate insulator has advantages in self-cleaning and a lower degree of fouling compared to the standard shape, in practical applications, 3-sheds-alternate insulators can be preferred, as using 3-sheds-alternate insulators with the same number of insulators has a greater safety margin.