High-frequency electromagnetic fields such as those associated with electromagnetic pulse (EMP) and intentional electromagnetic interference (IEMI) can couple to overhead power lines. Since the height of the overhead power lines can be comparable or even larger than the smallest wavelength of typical EMP and IEMI pulses, the classical transmission line approximation might not be suitable for evaluating the line response. On the other hand, a traditional full-wave solver (e.g., method of moments) is computationally inefficient, especially when dealing with long lines. To address these problems, we propose an efficient method to handle the high-frequency electromagnetic field coupling to overhead lines with nonlinear loads above a lossy ground. In the proposed method, the asymptotic approach is adopted and extended to the case of a lossy ground, which handles the problem in a semianalytical way and has a much higher computational efficiency in the case of long lines. Although the proposed method applies to the frequency domain, the case of nonlinear loads can be considered through a combination with the time-marching method. The proposed method is validated with several numerical examples.