Provided is a self-adaptive line selection method for a single-phase earth fault of a resonant earthed system. The self-adaptive line selection method for the single-phase earth fault of the resonant earthed system comprises the steps that when zero-sequence voltage of the system is greater than setting voltage, a fault line selection device is started and records bus zero-sequence voltage and zero-sequence currents of circuits before the fault and after the fault; atomic decomposition improved based on a PSO is carried out on the bus zero-sequence voltage, time of occurrence of the fault is determined, preprocessing is carried out on the collected zero-sequence currents of the circuits based on the time of occurrence of the fault to obtain transient state zero-sequence currents of two power frequency cycles, then the atomic decomposition improved based on the PSO is carried out on the transient state zero-sequence currents, and an optimal matched atom representing a transient state free oscillation component and a decaying direct current component of the transient state zero-sequence current of each circuit is obtained; corresponding characteristic information of the optimal matched atoms is extracted; according to the size of an energy entropy scaling factor, a single-phase earth fault occurrence mode is determined, and self-adaptive fault line selection is carried out according to the mode.