Abstract: Separated-zone water injection string in low-permeability oilfields is challenged by various problems after a long time in service, e.g. severe corrosion, scaling, and rapid decrease of separated-zone water injection conformity rate. To solve these problems, a digital separated-zone water injection string with a technology of cable-preset downhole flexible composite pipes was designed. The key tools, i.e. an intelligent water distributor and a cable-penetrated packer, were developed. Further, the key performances, including external pressure resistance and tensile strength, of the string were evaluated in laboratory. Separated-zone water injection technologies with flexible composite pipes suitable to downhole high-pressure were thereby developed. The laboratory evaluation results demonstrated that the developed string met the requirements on the packer setting pressure in separated-zone water injectors and the maximum external pressure resistance. The measurement error of the intelligent water distributor flow rate was below 2%. Field tests were carried out in four wells. The maximum service time was over 2 years, and the conformity rate of separated-zone water injection was 100%. This study indicates that the application of flexible composite pipes in cable preset digital separated-zone water injection technologies can effectively improve corrosion resistance, achieve automatic measurement and adjustment of separated-zone flow, remote sealing verification, and data monitoring, meet the requirements of packer setting, reverse circulation, and subsequent tests, all of which showcase promising application effects.