Abstract: The permeability coefficient of gas in municipal solid waste (MSW) is an important parameter for migration analysis and design of extraction well for gas in landfills. The permeability of MSW is mainly dependent on the void ratio, organic content, saturation degree and so on. In this study, the air permeability tests on unsaturated MSW are carried out under different influencing conditions by a new developed permeameter. It is found that there is a nonlinear relationship between permeability coefficient of MSW and seepage pressure of air, which can be better fitted by using the Forchheimer non-Darcy flow equation. With the increase of void ratio of MSW, the permeability coefficient increases, non-Darcy coefficient B_a decreases and the air pressure at demarcation point increases, respectively. With the increase of organic content in MSW, the permeability coefficient decreases and the air pressure at demarcation point increases, respectively. The flaky organic part will be spread and the connecting seepage path will be reduced in MSW, resulting in the attenuation of permeability for MSW. The higher the saturation degree in MSW, the smaller the permeability and the larger the air pressure at demarcation point. Within the effective porosity in the tests, there are better relationships among the permeability coefficient of MSW, the air pressure at demarcation point and the effective porosity, and the non-Darcy coefficients are changed in a narrow range.