Characteristics of sound absorption of mattress material in a sleeper electric multiple unit (EMU) was tested in the impedance tube based on the transfer function method. The finite element model of impedance tube to compute sound absorption characteristic was established with Delany-Bazley-Miki model to simulate the acoustic properties of porous absorption material. The experimental results accorded with the simulation results. Effects of thickness, porosity and the flow resistivity of mattress material in a sleeper EMU on sound absorption characteristics were analyzed. Increasing the thickness of the test sample will result an increase of the average absorption coefficient and the noise reduction coefficient (NRC), but the absorption characte ristics slightly change after the thickness increases to 70 mm. In the frequency domain, the sound absorption coefficient increase significantly with the increase of thickness in the low and middle frequency of 50～500 Hz. Increasing the porosity of the material will make the average absorption coefficient and the NRC increase, but not significant. In the frequency domain, the sound absorption coefficient increase significantly with the increase of porosity in the low and middle frequency of 100～800 Hz. The average absorption coefficient and the NRC both show a trend of decrease after the first increase and its peak appears around 0.5×105 Pa·s/m2 with the increase of flow resistivity. Compared to the original sample, the optimized sample mainly improves the frequency dependent absorption coefficient of 100～500 Hz, the average absorption coefficient increases by 12.85%, and the NRC increases by 16.69%.