The airflow modulator, which can generate the high-intensity infrasound, is a device transferring high-pressure gas energy into acoustic energy. Based on the aerodynamic theory, an airflow modulator is designed and the equivalent throat area formulas are deduced. Approximate theory is used to investigate the maximum sound pressure level, sound power, and airflow efficiency of this airflow modulator. The working mechanisms of the infrasonic acoustic generator consisting of a modulator and a Helmholtz resonator are studied by numerical simulations. In order to carry out the experiments, a prototype device was manufactured. It is shown that from the experimental results that this device can generate a continuous infrasound pressure level of 161dB in a 6 m 3 test cavity. The simulation and the experimental results are reasonably consistent and it is estimated that such a device can generate an infrasound pressure level in excess of 162dB below 3Hz.