Suitable for sampling of liquid medium with zero pressure and certain negative pressure, overflow and vacuum interface type, the outlet end is connected to a vacuum source, before sampling, the sample chamber is connected to the vacuum end for vacuuming, and the negative pressure of the medium in the sample chamber is assisted during sampling It flows into the sample chamber, and then enters the sampling bottle under the purge of inert gas. The system uses a gear box to control two ball valves at the same time, which makes the sampling process easier and safer for the operator.