A three-stage traveling-wave thermoacoustic engine (TWTAE) was designed and built,and the acoustic field was analyzed based on the linear thermoacoustic theory and the experiment. In the theoretical calculation,the acoustic field of the three-stage TWTAE is symmetrically distributed when the heating power of different stages is equal. In the experiment,the inconsistency of the acoustic field among three stages exists when the heating power is equal so that the acoustic field is not completely symmetrical. But the heating temperatures of three stages can be the same by controlling the heating power to ensure the acoustic field is basically symmetrical. Under this condition,the pressure phase difference between the corresponding positions of two adjacent stages is in the range of 120°±10°. With the increase of the mean pressure and heating temperature,the working frequency increases slightly and the change is not obvious,while the pressure amplitude and pressure ratio increase obviously. When nitrogen and helium are used as the working gas,the frequencies are about 20 Hz and 55 Hz,and the pressure ratios can reach 1.28 and 1.18,respectively.