Abstract: An acoustic metamaterial based on Helmholtz resonator with inner thin membrane is designed for controlling sound wave in low frequency range. By numerical calculation and analysis, it is concluded that an original Helmholtz resonator without thin membrane needs bigger geometric sizes to get better transmission coefficient curve in low frequency range, and its frequency band is very narrow. The transmission coefficient curve of the new designed acoustic metamaterial can show more minimal values in low frequency range, so that it can get better sound insulation effect in a wider low frequency range with the same geometric sizes as the original Helmholtz resonator. In addition, the geometric sizes of the acoustic metamaterial that affect the transmission coefficient are studied and the optimal geometric sizes of acoustic metamaterial are obtained.