Abstract: In Changqing Oilfield, the produced water currently presents serious corrosion and scaling behavior, shortening the service life of anti-corrosion steel tubing. In this paper, flexible composite pipes were developed for wells with different pipe diameters by carrying out mechanical calculation and structured material optimization. Then, string strength verification, finite element analysis and indoors performance evaluation were performed on the pipes, and a series of water injection strings were developed, which based on downhole flexible composite pipe and suitable for reinjection wells of produced water. They were tested on site in 32 wells, and the success ratio is 100%. So far, the longest water injection period is 4 years. Performance test was carried out by 12 well times. It is indicated that downhole flexible composite pipes have good anti-corrosion property, and they can increase the service life of water injection strings significantly. It is expected that the service life can be up to 10 years, which is 2 folds that of anti-corrosion steel tubing. And besides, the operation intensity and production cost can be decreased effectively. Therefore, this technology is promising in popularization and application.