When composite insulators are used in DC systems, how to choose the appropriate creepage distance becomes a big problem. This is due to the fact that there is too little research on the anti-fouling properties of composite insulators under DC resistance at home and abroad. Since the DC composite insulator has little experience in operation, the fouling law under various pollutions is not clear enough, and the data available for reference is too small. The third aspect of the problem is that the porcelain insulator is positive even under the same contamination. There is also a significant difference in the flashover voltage under the negative polarity, that is, there is a so-called polarity effect, and due to the influence of the polarity effect, the DC insulator flash voltage of the same shape and creepage distance is the same as the AC pollution flash voltage under the same contamination degree. The effective value is still low, that is, the orthogonal ratio is less than 1.0. Therefore, when the composite insulator is used in the DC system, the selection of the creepage distance needs to be paid special attention. There should be no frequent tripping caused by selecting the creepage distance according to the AC pollution flashing characteristics, and it is not necessary to blindly To increase the creepage distance too much, the shed skirt is too dense for the self-cleaning of the insulator, and it is easy to cause the bridging between the sheds, which may increase the pollution flashover and the wet flash voltage. Little, even counterproductive.