A method of using microphones to measure a particle velocity comprises steps: arranging a sound source, a first microphone and a second microphone in a space, wherein the first microphone is arranged between the sound source and second microphone, and wherein the first microphone is located at a first position and the second microphone is located at a second position more far away from the sound source than the first position; using the first and second microphones to measure the sound source and obtain first and second acoustic pressures respectively; using the first and second positions and an equivalent source method to establish a free-space Green's function, and using the first and second acoustic pressures and the equivalent source method to establish an acoustic pressure function; and using the free-space Green's function and acoustic pressure function to predict state space of sound amplitude and then obtain a particle velocity.