Abstract: The sheds structure of composite insulators is the important factor that affect icing process and icing flashover voltage. In order to study the icing characteristics of rime and the influence of shed structure on the icing process, the icing tests of 8 composite insulators with different shed structures were carried out at Xuefengshan natural icing test station. The results are as follows:the ice on windward edge is thicker than the middle part; the length of ice ridges on the windward side grows more slowly soon after the icing starts, then begins to accelerate for a period of time, then slows down again at the later stage and has a tendency to saturation. The ice on the leeward side is obviously thinner than that on the windward side, its growth rate shows a trend of first fast and then slow,and the thickness tends to be saturated. The thickest icing area of composite insulator is the edge of windward surface. The structural optimization design suggestions of composite insulator umbrella skirt in rime icing area are given : appropriately increase the top surface inclination; shed distance should be more than 40mm, and there should be more than three middle or small sheds between the adjacent large sheds; there shouldn’t be any edge under large, middle or small sheds, their diameters prefer to be 250/150/90 mm, and the arrangement can be “largesmall-middle-small-middle-small-large”.