Composite insulators have been used in power network systems for more than 20 years in China due to their remarkable anti-contamination performance. Compared to porcelain and glass insulators, the pollution flashover performance of composite insulators is better, whereas their icing flashover performance is still not clearly known. Shed configuration is a key factor that influences flashover voltage of composite insulators under icing conditions. In order to find relationships between icing flashover performance and freezing water conductivity, as well as shed configuration, experiments were carried out on ice-covered energized composite insulators, involving nominal voltages of 35 and 110 kV on different structures, at Chongqing University. When icing was light, the flashover performances of different shed configurations were almost the same. When icing was moderate, flashover performance was influenced by shed configuration parameters such as shed diameter, number of larger sheds, creepage distance and so on. When icing was heavy, the sheds were bridged and their configuration had little effect on the flashover performance. In order to explain the influence of shed configuration, the electric field distribution on composite insulators were also calculated by the finite element method (FEM). The calculation results were consistent with the experimental ones.