Abstract: A test system for measuring the gas permeation parameters of an ultra-low permeability medium in multi-field and multi-phase coupling conditions, comprising a triaxial permeation chamber, a deformation monitoring apparatus, a temperature sensing control apparatus, a volume/pressure controller, a bias stress loading apparatus, a gas injection apparatus, an outlet buffer container, and an ultra-low permeation flow monitoring apparatus. During the test, first applying temperature and triaxial stress control to a rock-soil mass sample; using the gas injection apparatus to inject high-pressure gas into the rock-soil mass sample; after permeation, the high-pressure gas enters the outlet buffer container and the ultra-low permeation flow monitoring apparatus to acquire the gas permeation flow; and, in the test process, the deformation monitoring apparatus can measure the local absolute deformation of the rock-soil mass sample.