To address the issues of insufficient sensitivity and narrow frequency band in traditional acoustic methods for partial discharge detection in power transformers, a high-sensitivity and wide-band Fabry-Pérot etalon (FPE) sensor is developed in this paper. By optimally the designed of etalon, collimator, and laser, the sensor achieves high sensitivity and wide-band response characteristics.The etalon is assembled using an optical adhesive method, ensuring that the parallelism error of the reflective surface is less than 2". In addition, a working point control method based on a solid etalon is designed, which effectively suppresses drift caused by temperature and light source fluctuations. Experimental results show that the FPE sensor responds well to partial discharge acoustic signals, with a sensitivity of 11.88 mV/Pa at 50 kHz and a measurement bandwidth from 10 kHz to 1 MHz. Its frequency response performance is close to that of the reference acoustic sensor Eta250 and superior to the 4939-A-011 acoustic sensor. Meanwhile, its measurement sensitivity is higher than that of both Eta250 and piezoelectric sensors, approximately four times that of the 4939-A-011 acoustic sensor. The development of this sensor provides a new optical acoustic sensing technology for partial discharge detection in power transformers. Owing to its strong anti-electromagnetic interference capability, wide-band detection, and high sensitivity characteristics. It can effectively improve the accuracy of insulation defect location, offering important technical support for enhancing the accuracy and reliability of transformer insulation condition monitoring.