Optical fiber sensors (OFS), leveraging their intrinsic insulation and high sensitivity, hold significant potential for partial discharge detection in electrical equipment. To achieve high-sensitivity partial discharge detection, this paper proposes the OFS based on heterodyne interferometry. By introducing frequency shift in the reference arm of the intrinsic interferometric system using an acousto-optic modulator (AOM), the output signal is shifted away from the low-frequency region, which is typically dominated by noise. The OFS test platform was constructed to evaluate the detection performance of the OFS. For partial discharge detection in a typical model, the signal-to-noise ratio (SNR) of the OFS response waveform was 3.6 dB higher than that of the piezoelectric transducer (PZT). In the frequency domain, the OFS demonstrated a wider detection bandwidth and richer frequency information, enabling effective detection of signals in the 20 kHz to 80 kHz range. The results indicate that the developed OFS outperforms existing PZT sensors in detection performance and can serve as a valuable complement to current partial discharge detection methods for electrical equipment.