The invention discloses an automatic tail gas separation and purification system on an air extraction system of a superconducting tokamak device. The system is characterized in that a primary air storage tank inflates gas into a porous gas separation chamber through a pipeline and an inflation valve, and an air extraction unit transfers gas in the porous gas separation chamber to the primary air storage tank through an air extraction pipeline and an air extraction valve door, so as to enable the gas pressure in the porous gas separation chamber to be kept at a specified gas pressure value; thecryogenic pump pumps out gas leaked from pores of the porous gas separation chamber from a vacuum chamber body through the valve door and a connecting pipeline, and the cryogenic pump can return to temperature after tail gas separation is completed. The tail gas is automatically separated by adopting a leakage flow principle, and the mixed gas in the porous gas separation chamber is selected withan appropriate pore size and an appropriate working gas pressure; and due to a leakage flow effect, small-mass molecules are easy to flow out of the pores, while large-mass gas molecules are not easyto flow out, so that the effective separation of the large-mass molecules and the small-mass molecules can be conveniently realized.