A novel fiber-optic sensor with dual Fabry-Perot(F-P) cavities was reported to detect the Acoustic Emission(AE) signals induced by the damage in composite and metal materials. A sensing model for detecting the AE signals of the fiber-optic sensor was established based on the multi-beam interference principle of the low finesse F-P cavity. The operating mechanism for stabilizing the quadrature-point of the dual F-P cavity sensor was analyzed, and then the fiber-optic sensor with a dual F-P probes was designed and manufactured to maintain the stability of the quadrature-point. The operating performance of the designed sensor was verified by two types of experiments on simulating AE signal detection and thermal stress interference experiments. In the first experiment, two kinds of AE signals were generated by shock vibration and breaking pencil leads and they were detected and compared with a piezoelectric sensor and a optical fiber sensor. The test results show that the optical sensor successfully measures the simulated two kinds of AE signals and it possesses a sensitivity of 12.9 nm and a frequency response of 30 kHz. In the second experiment, the stability of operating points of the sensor was detected, and the results indicate that control mechanism of the dual F-P cavities ensures the sensor to operate at the quadrature-point, and overcomes the signal attenuation of the sensor outputs.