Abstract: Anechoic chamber and hemi-anechoic chamber provide the necessary acoustic environment for various acoustic tests, mainly including frequency range, spatial range, and background noise of the free sound field. The anechoic chamber and hemi-anechoic chamber absorb the sound wave incident on the wall and reduce the reflected sound by laying sound-absorbing materials in the chamber, thereby generating a free sound field environment. This paper introduces the principle and method of calibrating the free sound field of anechoic chamber and hemi-anechoic chamber by inverse square law and the data processing of the free sound field of the anechoic chamber to provide experience reference for improving the measurement accuracy of the free sound field of anechoic chamber.