Abstract: After the damage of casings in the water injection wells, injected water easily flows into the inefficient formation through the damaged part of casings, thus, the corresponding oil well production decreases and the surface energy consumption of water wells increases. Most oilfields use "packer setting" method for separate layer water injection. However, flushing fluid easily leaks into the formation through the damaged part of casings during inverse well flushing, so the purpose of cleaning well bore and formation can not be attained. To solve these problems, the pipe string with the technology of stuck sealing and separate layer injection for casing damaged wells and effective inverse well flushing was studied by using the design principle of double injection pipes. The key tools used double-layer design of inner and outer pipes with normally injected water flowing in the inner pipe and inverse well flushing water flowing in the outer pipe. Hence, the separation of normal water injection channel and inverse well flushing channel was achieved. This technology pipe string has been applied in the field for 5 well times. The maximum inverse well flushing pressure reaches 4.0 MPa and the maximum discharge capacity of inverse well flushing reaches 25 m³/h. The inverse flushed wells have no leakage and good application effect has been obtained. Therefore, this pipe string can meet with the field process requirement.