Abstract: Traditional fiber optic acoustic emission (AE) sensors used for power equipment partial discharge (PD) detection are still unsatisfactory in engineering due to the sensitivity, media compatibility, and difficulty in spatial separation from the demodulation system. The linear cavity fiber laser (LCFL) has ultra-high detection sensitivity because of its ultra-narrow linewidth emission. Moreover, the small size of LCFL and its independence from the demodulation system may effectively solve the above problems. This paper proposes a PD AE detection system using LCFL as the sensor. Then, the installation position of the optical isolator is determined in the A regime (0~200.6m) of external optical feedback (EOF) coefficient based on the EOF theory of semiconductor laser to suppress the EOF noise introduced by the intrinsic light source property of LCFL in the long-distance application. The average noise of the improved system in long-distance detection is reduced by 87.49%. The experimental results of 80kVA oil-immersed transformer PD long-distance detection show that the PD detection system could be effectively applied in PD long-distance detection with sizeable ultrasonic attenuation. The average maximum response amplitude of the system is 1354% higher than that of the piezoelectric transducer (PZT) sensor during the same AE excitation, and the system stability is much better than PZT.