Partial discharge (PD) detection plays a pivotal role in ensuring the integrity and reliability of electrical power systems. PD events serve as precursors to insulation breakdown, posing significant threats to equipment safety and operational continuity. Traditional PD detection methods have exhibited limitations, particularly in liquid insulation environments. This chapter presents an interferometric method for detecting PD in liquids. Employing a setup based on interferometry, PD in the liquid sample is induced by the voltage from a lightning surge generator, and the resulting distorted interference patterns are captured using a CCD camera. The experimental results show that the peak value of the phase after PD is larger than that before PD, and the peak value of the phase distribution increases accordingly with the increase of the voltage. This study highlights the direct relationship between the applied voltage and the phase distribution generated within the interferogram, which provides a new idea for condition monitoring and fault diagnosis of liquid insulation systems.