The utility model provides a water injection packer and water injection string relates to the oil development technique. The water injection packer includes: center tube, setting mechanism and backwashing valve subassembly, setting mechanism is last to have the well -flushing delivery port, and the well -flushing water inlet has been sheathe in to the pneumatic cylinder of backwashing valve subassembly, and the well -flushing delivery port forms the well -flushing passageway with well -flushing water inlet intercommunication, the tail end of center tube has the valve body, formation effect chamber between valve body and the backwashing valve subassembly, there are feed liquor valve module and relief valve assembly in the valve body, feed liquor valve water inlet and center tube intercommunication on the valve body, feed liquor valve delivery port and effect chamber intercommunication, relief valve water inlet and effect chamber intercommunication, relief valve delivery port and center tube intercommunication, when reaching the second default with the pressure at the effect intracavity, close the feed liquor valve module, open relief valve assembly, liquid reflux to the center tube of feasible effect intracavity, the pressure in effect chamber, it helps backwashing valve to break away from the backwashing valve seat down to reduce, thereby well -flushing pressure has been reduced, guarantee the backwashing valve subassembly is opened smoothly.