Abstract: The present study aims to explore the icing characteristics of catenary cantilever insulator at extremely low temperatures. To begin with, the icing test is carried out in the artificial climate chamber to determine the icing morphology of the cantilever insulator. By taking into account the test results, a 1:1 three-dimensional model is then established to analyze how the local electric field distribution is affected by the length of the icicle and the hanging water droplets at the end of the icicle. Finally, the structure of insulator sheath is optimized. According to the analytical results, when the cantilever insulator is installed at a certain angle, there is an air gap arising between the small sheath icicle and the adjacent large sheath surface as well as between the large sheath icicles. The air gap acts as a strong electric field, with the rate of field strength distortion reaching 621%. After the air gap is eliminated, the large and small sheathes are connected, thus resulting in the partial failure of creepage distance in the insulator. When the ice layer on the surface of the sheath melts, the tip of the icicle tends to form a suspended droplet, causing distortion to the electric field in the surroundings. At this time, the rate of field intensity distortion as caused by the droplet can reach 4 977%. The sheath of an extraordinary shape can serve as an effective wall icicle bridge sheath to increase the spacing of air gap, thereby reducing the amount of icicle on the insulator around the place where electric field is distorted.