An annular ejector of an annular jet pump is coaxially arranged at a front of a central ejector. The annular ejector includes an annular nozzle, an annular mixing chamber, and an annular mixing duct. The central ejector includes a central nozzle, a central mixing chamber, and a central mixing duct. The annular nozzle is connected with a primary fluid inlet. A primary fluid inlet is in direct connection with the central nozzle arranged at a bottom of the central pipe, and a secondary fluid inlet is connected with a sidewall of the annular mixing chamber.