The invention discloses a fluid on-off method and a fluid on-off device which are good in safety and stability. Due to the adoption of the fluid on-off method and the fluid on-off device, cutoff is conducted through the whole device, and main pressure is not borne by a single place. The fluid on-off method and the fluid on-off device overcome the defects that the prior fluid on-off device needs to use a closure member which is easy to damage. The fluid on-off device comprises a high liquid level connector and a lower liquid level connector. At least one cavity is placed between the high liquid level connector and the lower liquid level connector. Cavities are sequentially communicated. Fluid which is closured is filled in the cavities. Each cavity further comprises an air seal section which separates the fluid in the cavities into front fluid sections and rear fluid sections. The heights of the front fluid sections are larger than those of the rear fluid sections. Air-charging and air-discharging openings are placed on the top of the cavities. The fluid on-off method and the fluid on-off device are suitable for applicative occasions of the prior fluid on-off device, and have the advantages of being capable of automatically dredging and reducing pressure, high in safety and stability and the like.