Abstract: To improve the electromagnetic working environment of the 330 kV segmented composite insulator,optimize the voltage-sharing structure and configure the proper voltage-sharing scheme,we use 3 D finite element software for modeling and analysis,comparing the relationship between large grading ring parameters（the ring diameter,pipe diameter and cover depth） and the surface field strength, selecting the parameter configuration by comprehensive consideration,and optimizing the parameters of the small grading ring on the basis of determining the size of the large grading ring,and the following reasonable parameters of the grading structure are obtained: the ring diameter,pipe diameter and cover depth of the large ring should be 350 mm,50 mm and 125 mm respectively,and those of the small ring be 100 mm,25 mm and 20 mm respectively. The scheme can effectively improve the uneven distribution of the surface field intensity of the voltage grading ring and composite insulator,which can be used as a reference for practical engineering.