The partial discharge（PD） measurement is an effective technique for the detection of insulation defects and provides data on the condition maintenance. On-line PD measurement is currently affected by the electromagnetic interference， which makes sensitive PD detection very difficult. In this paper， an optical current sensor based on the Faraday magneto-optic effect with a double solenoid structure is applied in the PD detection， enriching the content of the PD detection and breaking through the limitations in the current method. Four PD models have been developed， and the characteristic of the optical path loss and the anti-interference capability of sensor are studied using Malus'law and Ampere's law. The continuous wavelet transform theory is used to analyze the time-frequency characteristic of PD signals. The comparison results with other sensors show that the optical current sensor has superior performance， providing a basis for further application of the optical method in PD measurement.