Abstract: In order to solve the bad low frequency sound absorption of the Micro-Perforated panel (MPP) absorber, mechanical impedance was introduced in the back of the MPP absorber to form a composite structure. According to the same particle vibration velocity on both sides of a plate, the mechanical impedance plate transfer matrix could be obtained. The units of the mechanical impedance, cavity and MPP were connected ix series with the use of the transfer matrix method, thus creating the composite structure's theoreticM calculation model. The quality factor affecting absorption bandwidth was analysed. Bandwidth is inversely proportional to the mechanical impedance plate mass. During the experiments, when at close to 400 Hz, the composite structure reached an absorption peak with a coefficient of above 0.8. Experimental results concurred with theoretical calculations. Mechanical resonance is added based on the traditional MPP resonance sound absorption mechanism. Through this, the performance of low frequency sound absorption can be improved without increasing the thickness of the structure. The frequency band can be broadened by redncing the mechanical impedance plate mass and controlling its boundary-damping coefficient.