Abstract: Reverberation chamber method and the standing wave tube method are two main traditional methods to measure the sound absorption coefficient． But they are easy to be limited by experimental conditions and have some limitations in practical engineering applications． Based on the vector characteristics of the measured three-dimen-sional sound intensity，a four-microphone was used to calculate the corresponding sound absorption coefficient by measuring the amplitude of the sound intensity reflected by the tested specimen and the total reflector plate，re-spectively． This method can not only measure the absorption coefficient of materials，but also measure the inci-dence angle and reflection angle of sound waves． Firstly，the principle analysis of the measurement of the sound absorption coefficient was carried out by the three-dimensional sound intensity method． Then the software was used to simulate the system，and the measurement errors of the absorption coefficient in different frequency band，diffe-rent absorption coefficient and different incidence angle were discussed． At last，the method was used to measure the three materials，and the results were compared with the results of standing wave tube method，and the directivi-ty error was tested． The results show that the error range of the absorption coefficients of 630 ～ 4 000Hz measured
by this method and the standing wave tube method is ± 0. 02 ～ ±0. 10，the directivity error is between 1 ° and 6 °，and the directivity error of different incident angles from 0 ° to 80 ° is between 1 ° and 3. 5 °．

Key words: three-dimensional sound intensity method, standing wave tube method, sound absorption coefficient, oblique incidence, measurement accuracy, directivity error, incidence angle