Based on multi-beam interference principle,an extrinsic fiber Fabry-Perot (FP) sensor was developed to measure the acoustic signal in liquid,whose interference cavity was consisted of quartz diaphragm,end of pigtail and air film.The sensitivity,amplitude-frequency and the output signals of the sensor were analyzed.The parameters of FP sensor were obtained to analyze amplitude-frequency characteristics of quartz diaphragm theoretically and experimentally.Finally,a measurement system on acoustic signals in water was developed and the effect of operation points on output signals were discussed and tested in different conditions.The experimental results indicate that the extrinsic fiber FP acoustic sensors in proposed system are able to measure acoustic signal in the liquid.Its fundamental frequency can reach to 140 kHz and sensitivity is 0.005 nm/Pa.The characteristics of output signal of the sensors are dependent on operational points and modulation depths of input signal.The sensitivity of the sensor is optimial when the operational points lie in quadrature point of operation curve.the measurement region will be increased when the output signal is frequency double for over modulation.