The recovery voltage of the fault phase during occurrences of single-phase temporary faults in EHV/UHV transmission lines with series capacitors is composed of the components of power frequency, approximate power frequency, and low frequency. The power spectrum of the recovery voltage possesses three spectral lines. However, the recovery voltage of single-phase permanent fault only contains power frequency and low frequency components, and its power spectrum possesses two spectral lines. On this basis, an identification method of temporary and permanent single-phase earth fault was proposed for the transmission lines with series capacitors. Simulation results showed that the proposed method based on power spectrum of fault phase recovery voltage was accurate and feasible.