The external air source interface is installed at the waist of the protective clothing. It is the only one-way valve that communicates with the inside and outside of the protective clothing; Outer connector: male connector, which can be connected to a mobile gas supply source to get external gas to supply gas into the protective clothing; Inner connector: female head, which can be connected to the rescue port of the empty breather carried by the user, and provides air supplied by the external mobile air supply source to the empty breather, so as to save the amount of empty breather bottles and extend the working time; Inner joint: female, connected with the air pipe of the built-in air circulation system to transport gas.