Abstract: To solve the problem of frequent replacement of expandable zonal water injection string due to expansion packer damage or bottom ball valve leakage, a cylinder-type expansion packer with relatively independent internal and external pressure systems was developed in accordance with the principle of hydraulic transmission. According to field practices, a combined sand flushing valve and leak-proof device was developed to ensure positive sealing and to reduce the influence of bottom ball valve leakage on the performance of a zonal water injection string. An expandable zonal water injection string with balanced force was designed based on a cylinder type expansion packer. It combined with sand flushing valve and leak-proof device to form a long-term expandable zonal water injection technology. This technology was applied in more than 100 wells in the Shengli Oilfield, and proved to be continuously effective. The field application results show that this technology can effectively solve the problem of integral failure of expandable zonal water injection strings caused by expansion packer damage and bottom ball valve leakage, thus improving the development efficacy of water injection.