Numerical simulations were carried out based on the software Sysnoise and Fluent.And it also puts forward a muffler structure of impedance, raises methods to calculate the property of a muffler through which the medium is the mixture of gas and water, and forecasts the transmission loss and flow resistance of the muffler and then prove it by verification test. Experiment results fit the calculations very well in low frequency. Uniform mixing of gas and liquid makes the noise reduction frequency higher, thus the property of the muffler become worse in low frequency. Water held up on the surface of the inner tube makes the muffler function well in low frequency.