A series of tests on undistured dry soil and remoulded Malan loess were conducted by using improved ZC-2015 air permeameter. Gas permeability experiments analyzed the effects of soil volume, permeability diameter, dry density and sampling depth on air permeability (ka), and loess permeability was explained by the pore structure parameters, which were obtained by electron microscopy in SEM tests. The results showed that ka was not only a quantitative index of the gas seepage, but also was an important parameter that describing the pore and structure characteristics of unsaturated Malan loess. Due to the size effect in different soil volumes of loess, and their permeability increased with the increasing of volume of soil samples. In addition, ka decreased with the increasing of dry density and permeability diameter. Comparing the test results and the SEM photographs of three different types of Malan loess, and combined with the statistics of the pore structure parameters, we can conclude that ka has a certain regularity in area and depth. Regionally, the content of clay particles in the soil particles increased, while the total pore and macropore area decreased, and the effective seepage porosity decreased, and ka of remolded soil with the increase of soil depth has a little decrease.