Abstract: A system for preparing nanoscale zero-valent iron by reverse filtration in a non-open inert atmosphere is provided including an inert gas bottle, a gas monitoring and buffering device, a main reaction device configured as a three-necked flask, a condensing device including a condenser tube and a cold source, a waste liquid collecting device configured as a waste liquid collecting bottle, a liquid sealing device including a second liquid sealing bottle connected with the waste liquid collecting bottle through a first connecting-pipe, and an extraction pressure adjusting device including a third triple valve and a vacuum pump, all of which are connected by pipelines in sequence. Three necks of the three-necked flask are respectively provided with a first triple valve, a single-hole rubber plug pierced with a liquid-taking pipe, and a second triple valve. The second liquid sealing bottle is connected with the third triple valve.