Abstract: The sound pressure source generated by the resonant coupled tube method has a high sound pressure level with a low distortion. It is usually used for the calibration of level linearity and distortion of high sound pressure microphones at a fixed frequency. Based on the acoustic finite element model, this paper analyzes the characteristic frequency and frequency response of a resonant coupled tube, and optimizes the design of the tube. The experimental value of the resonant fundamental frequency differed from the calculated value by 0.8 Hz. The resonant coupled tube at 500 Hz generated a sound pressure level of 174 dB with a total harmonic distortion of 0.5%.