The AC flashover performance of 110 kV iced potential transformer is investigated by testing in laboratory to analyze the influence degree of icing on the safe and reliable operation of power system. The results show that the AC flashover voltage of 110 kV iced potential transformer decreases with the ice amount increasing. The relation between icing flashover voltage and ice amount accords with the negative exponential function law, and the characteristic index is in the range of 0.085～0.100. Meanwhile, the relation between icing flashover voltage and ice thickness accords with the negative power function law, and the characteristic index is in the range of 0.40～0.55. The flashover voltage of 110 kV iced bushing is related to the pollution before icing. The relation between icing flashover voltage and salt deposit density (SDD) accords with the negative power function law, and the characteristic index is in the range of 0.21～0.26. When the ice thickness is up to 25 mm and SDD is 0.08 mg/cm2 and above, the icing flashover occurs on the 110 kV potential transformer in service. The effective measures to prevent AC icing flashover of 110 kV potential transformer are to increase the height of the structure and install creepage extenders. The results can offer consults for the external insulation selection and design of substation in ice covered regions.