Abstract: The mathematical model of micro-perforated sound absorption structure in water medium was established using mode superposition method,and the electro-acoustic analogy based equivalent circuit model was obtained.The influence of the vibration of Flexible Micro-Perforated Panel(FMPP) and Flexible Back Panel(FBP) on the sound absorption coefficient was studied.Because structural impedance of micro-perforated panel in water,different from that in air medium,was not sufficient to acquire the sound absorption effect,a strengthened micro-perforated sound absorption structure was proposed,and was verified in the water medium impedance tube.The results showed that,the average absorption coefficient of the strengthened micro-perforated panel in the range of 20,2000 Hz was improved and converged to that of rigid micro-perforated panel with the increase of bending stiffness.The absorption peak of Flexible Micro-Perforated Panel Cavity with Flexible Back Panel(FMPPCFBP) was shifted to the lower frequency,and sound absorption effect in low frequency was improved as well.