Fiber-optic sensor have excellent resistance to electromagnetic inter ference,passive, and corrosion resistance,and is suitable for harsh environments such as flammab le and explosive, strong electromagnetic interference,and underwater.This paper proposes a fiber -optic acoustic sensor based on the principle of reflective intensity modulation to achieve the modulation of acoustic wave on light intensity.A sensing structure is designed for the propos ed fiber-optic sensor.The fiber collimator is adopted to receive and transmit optical signals, and the retroreflective material is used to design the vibrating membrane.Based on the focusing principle of the fiber collimator and the retroreflective principle of the membrane,the r eceiving angle of the optical beam is effectively enlarged to achieve high fault-tolerant meas urement of the sensor and improve the sensor stability.The mathematical model of the sensor is researched and simulated.The sensor is fabricated and tested.The experimental results show th at the proposed sensor can effectively detect specific frequency band acoustic signal and especi ally respond well to acoustic waves with a frequency of about 1000Hz.The propo sed sensor has the advantages of long working distance,strong structural fault tolerance and strong ability to r econstructed acoustic signal,and it can be applied to areas such as defense security monitor ing.