The invention discloses a gas isolation device and isolation method. The gas isolation device and isolation method is used for preventing a pollutant in a low cleaning cavity from diffusing towards ahigh cleaning cavity. The gas isolation device is of a pipeline structure with two opening ends, wherein a wide opening end is connected with the high cleaning cavity, a narrow opening end is connected with the low cleaning cavity, two layers of inflatable holes are formed in a side wall of a surface of the gas isolation devices and are used for inflating an isolation structure, and a layer of extraction openings are formed in a side wall of an opposite surface and is used for extracting a part of gas in the isolation structure. By dual suppression effects of gas flow on pollutant diffusion and a carrying and removal effect of the gas flow on the pollutant, the pollutant diffusion is prevented better.