Abstract: The measurements of the absorption coefficient of sound absorbing materials are mainly using the standing wave tube or the reverberant room.Both of them are belong to laboratory methods,which are not suitable for measurement in situ.The normal loudspeaker reflection method can measure the absorption coefficients in situ.However, it has limitations on the size of the material and the measuring room.Based on the high directional property and the plan wave property of the self-demodulated sound from parametric array,under the excitation of sweep frequency sound wave,the absorption coefficients of the material are measured in free field and normal room.The testing results are compared to the standing wave tube method,which shows it is able to measure the absorption coefficients in situ rapidly without the standing wave tube or the reverberant room.