Abstract: The acoustical characteristics of resonator on Erhu are presented in this paper. As compared with Jinghu, the resonant frequency of air in the resonator-cylinder and membrane system is much lower than the quarter wave-length resonanece frequency of the cylinder. The lowest resonant frequency of the membrane is about two octaves higher than this frequency. The frequency range of the resonator is mainly between one and 4.6 times of this frequency. Frequency responses in the cases of impulse excitation on the string and bowed string are given The sound spectra obtained by playing seven notes on inner and outer strings can be used as the frequency characteristics of Erhu sound.