The invention provides a sewage reinjection well. A corrosion-resisting casing pipe used for injecting water is fixedly installed in the well, and the inner wall of the corrosion-resisting casing pipe is coated with a corrosion-resisting coating. The lower end of the corrosion-resisting casing pipe extends to the water injection layer, and cement of the corrosion-resisting casing pipe extends to a well mouth. The invention further provides a water injection method of the sewage reinjection well. By means of the sewage reinjection well and the water injection method of the sewage reinjection well, an oil pipe can be prevented from being corroded after water is injected, and therefore cost is reduced; in addition, the water injection efficiency can be improved, and power consumption is reduced.