Abstract: As an important component of ultra high voltage converter station, AC filters play a role in reactive power compensation and harmonic filtering, and have a significant impact on the stable power transmission of ultra high voltage converter station. Capacitors are one of the important components of AC filters, with Large installation quantity, and are prone to faults such as excessive capacitance and joint heating. This article proposes a new unbalanced current testing method that can significantly reduce operational intensity and risks.