[Objective] To improve the calculation accuracy of the jumper length for six-bundle jumpers in ultra-high voltage direct current （UHVDC） transmission lines and to efficiently achieve prefabricated installation of the jumpers， a precise calculation method for the inclination angle at the end of the tension string and the jumper length is proposed. [Methods] Taking the horizontal tension of the conductor as the reference， the inclination angles of individual connecting components are analyzed sequentially， and the inclination angle at the end of the tension string is calculated using an iterative method. A general calculation model based on a three-dimensional coordinate system is established， and the jumper length is calculated using the catenary formula under the condition that the sag of each sub-conductor of the flexible jumper is uniform. The accuracy of the inclination angle at the end of the tension string， the general calculation model， and the jumper length calculation method is verified using finite element simulation， three-dimensional modeling in AutoCAD， and field measurements. [Results] The proposed iterative method achieves a stable terminal inclination angle after four iterations， and the calculated inclination angles are in good agreement with the finite element simulation results. The suspension points of each jumper obtained using the proposed general calculation model are consistent with the simulated positions generated by AutoCAD modeling. After the prefabricated installation of an actual jumper， field measurements obtained via total station and drone surveys closely matched the calculated values. A jumper installation case demonstrates that， compared with the traditional high-altitude simulation method， the prefabricated approach reduces high-altitude workload by 46.4%， increases work efficiency by 25%， and reduces labor costs by 33.3%. [Conclusions] The proposed iterative method for calculating the inclination angle of the tension string is more accurate than the traditional method that simplifies the tension string as a uniformly distributed self-weight load. The general-purpose program developed for calculating the length of six-bundle jumpers features good graphical user interaction and offers strong practicality and convenience. The prefabricated installation of six-bundle large-cross-section conductor jumpers for UHVDC transmission lines has been successfully realized， achieving the objectives of reducing high-altitude workload， improving construction efficiency， minimizing conductor loss， and ensuring high quality of construction technology.