In the prestressing system of nuclear island containment structures, steel tendons with stress measurement devices are installed to monitor the prestress loss during the construction and operational phases of nuclear power plants. As the effective corrosion protection for monitoring tendons is vital, wax injection techniques for monitoring tendons were explored in this study. By analyzing the critical aspects and challenges therein, selecting anti-corrosion materials and injection devices, and conducting verification tests and on-site construction, the construction processes of wax injection were determined and the effectiveness of domestic equipment was verified. During the wax melting process, stirring can significantly shorten the time it takes for the wax to fully melt. During wax injection, the wax temperature should not be lower than 65°C and should not exceed 130°C. To achieve good injection effect, the injection time should not exceed 30 minutes, with 10 minutes being optimal. Several conclusive findings were proposed and might be useful for engineering practice.