Response properties of the fourth-order acoustic low-pass filtering fiber-optic hydrophones are investigated theoretically and experimentally. A mechanical acoustic resistance， which is used to describe the system’s mechanical loss， is introduced into the previous lumped parameters model of the hydrophone， and an improved acoustic equivalent circuit is given. Phase frequency response is an important parameter for the hydrophone array applications. It has great effect on beamforming， which affects the abilities of locating， discerning， and tracking targets. Therefore， the phase response peroperties is studied with the amplitude response peroperties. Some results， which are instructive for designing of acoustic low-pass filtering hydrophone， are obtained by numerical simulation. The measured rsponse curves are in good agreement with the simulation results， which verifies the correctness of the theory and the model. The fourth-order acoustic low-pass filtering fiber-optic hydrophones are useful for improvement of the anti-aliasing ability of modern sonar arrays.