Abstract: The permeability coefficient is an important parameter in the study of loess seepage deformation and loess hydraulic properties. However,the gas permeability coefficient has a good correlation with the permeability coefficient,and water sensitivity of loess can not affect its testing process. At the same time,it is more convenient and faster than the determination of permeability coefficient. So it has a good prospect of popularization and application. This paper introduces the principle of loess in-situ gas permeability test method. On this basis,we carry a series of in-situ gas permeability tests in different loess areas by contact type and plug-in type. The test results show that the two methods have different application scopes for loess stratum. The plug-in method is more suitable when the clay content of loess is greater than 12.44%(the plasticity index is greater than 11.2). On the contrary,when the clay content is less than 12.44%(the plasticity index is less than 11.2),the plug-in method can cause larger errors. The comprehensive comparison shows the contact method is generally applicable to loess strata because of its less human error. But this method needs a larger working face and is more suitable for horizontal working face,which affects the test speed and convenience. The plug-in method needs a smaller working face,and is suitable for both horizontal and vertical working face. So it is more convenient and faster. However,the process of probe inserting into loess can cause disturbance,so this method is more suitable for loess layer with higher clay content. When the clay content of loess is greater than 12.44%(the plasticity index is greater than 11.2),we suggest to give priority to the plug-in method. If the site does not meet these conditions,we suggest to choose the contact method. The two determination methods of in-situ gas permeability coefficient of loess and their application scope provide a theoretical basis for further application in practice.