To illustrate the electromagnetic scattering characteristics of ultra-high-voltage power transmission line when it is illuminated by high-resolution synthetic aperture radar satellite working at X-band frequencies, the geometric structure and the material properties of ultra-high-voltage power transmission lines were first analyzed, and a physical model was developed for power lines based on the catenary equation. Then, the electromagnetic scattering characteristics of ultra-high-voltage power transmission line at X-band frequencies were analyzed, where the Helmholtz equation in cylindrical coordinates was solved to obtain the two-dimensional diffraction coefficient and, subsequently, the incremental length diffraction coefficient method was employed to acquire the three-dimensional diffraction coefficient and the radar cross section (RCS). Finally, taking into account different polarization modes and diameters of power line, the calculation results of the RCS of power line were compared with the measured anechoic chamber data. Analysis results show that a maximum mean error of 8.1% could be achieved for different diameters of power line, which preliminarily confirms the correctness of the proposed method when it is used for analyzing the electromagnetic scattering characteristics of ultra-high-voltage power transmission line at X-band frequencies.