The acoustic sensitivity of mandrel interferometric fiber-optic hydrophone with three layers(coated layer,flexible tube,mandrel) was analyzed. Modeling was built with three-dimensional elasticity analysis. Results show that the major factors which influence the acoustic sensitivity of the hydrophone are elastic modulus,wall thickness,outer radius of the tube,and sensing fiber′s length and diameter. Young′s modulus,Poisson′s ratio and thickness of encapsulation layer and mandrel have little effect on the acoustic sensitivity. A number of hydrophone samples were produced. The theoretical value of their acoustic sensitivity is -150.7 dB (re rad/μPa),and the average measured values is -151.3 dB (re rad/μPa). The range of measured values is -151.9~-150.5 dB (re rad/μPa),the difference between theoretical value and the measured value is less than 1.2 dB(re rad/μPa). Experiments also show that encapsulation process of packaging has some influence on the acoustic sensitivity.