The utility model discloses a water injection device of hyposmosis oil reservoir, including the water supply well, filter jar, sterilization tank, charge pump, jar body, the delivery port of charge pump is through a pipeline and jar body one end intercommunication of intaking, a jar body other end is connected with the water injection pipe, the interval is provided with baffle and shutoff board on the inner wall of jar body one side, installs a plurality of the 2nd sacrificial anode on the opposite side inner wall is personally experienced sth. Part of the body to the jar, telescopic both ends are run through respectively baffle and shutoff board, a plurality of sacrificial anode fix in the annular space, and it has the hole of permeating water a plurality of and the annular space intercommunication to open on the baffle, and it has opening a plurality of and the annular space intercommunication to open on the sleeve is close to the one end outer wall of shutoff board. Adopt stage treatment in the processing to the injected water, prevent the corruption in the primary treatment cavity, and carry on main anticorrosively in the secondary treatment cavity for jar internal sacrificial anode's work load greatly reduced avoids a jar internal sacrificial anode quick consumption and frequent the change to appear, reduces the manufacturing cost in the oil development in -process water injection process.