The traction power system is utilized for powering high-speed railways. However, the lightning arrester on the roof of the EMU poses significant challenges to its safety and stability due to transient overvoltage and high harmonic content during operation. This paper aims at measure the operating conditions of the EMU, with main harmonics identified at 25, 27, and 29. Subsequently, an accurate simulation of actual voltage is conducted to carry out an aging test on ZnO varistors. The results show that after aging, the nonlinear coefficient of the resistor increases from 29.86 to 43.26 while the leakage current density decreases from 2.23μA/cm2 to 1.40μA/cm2. During aging, neutral zinc intercalation Zni× continuously accumulates at grain interfaces which reduces grain boundary barriers and leads to a decrease in macroscopic electrical performance as evidenced by lower leakage current density levels observed. These findings provide valuable data support for enhancing ZnO varistor stability under complex high-frequency conditions and contribute towards further understanding of its aging mechanism.