Accreted ice on conductors in transmission lines may cause mechanical and electrical faults to power grid system, leading to the fact that the determination of designed ice thickness on conductors plays an important role for the safe operation of power grid. When determining the designed ice thickness of conductors in transmission lines, the standard ice thickness on different diameters should be computed to the specific diameter with using diameter correction formula. Related ice data was acquired through experiments in artificial climate chamber, and the diameter correction coefficients of conductors were fitted respectively according to different types of accreted ice. The results show that the conductor diameter correction coefficients of rime and mixed-phase icing decrease with the increase of conductor diameter, and the decreasing trend of the correction coefficient of rime is larger than that of mixed-phase icing; the conductor diameter correction coefficients of glaze icing increases with the increase of conductor diameter.