To improve the accuracy of fault location in the case of single-phase grounding faults in distribution networks, a method for fault line selection and location based on the voltage zero-mode traveling-wave S-transform time-frequency matrix is proposed. First, the traveling-wave signals measured by the traveling-wave detection devices at the ends of each feeder are decoupled to obtain the fault voltage zero-mode traveling wave. Then, faults are set at special locations such as the main feeder, primary and secondary branch lines to obtain the S-transform time-frequency matrix corresponding to the fault location, and a comparison library for determining the fault branch is established. Finally, the S-transform time-frequency matrix of the fault zero-mode voltage traveling wave is compared with the data in the comparison library for similarity to determine the feeder and branch where the single-phase grounding fault occurs. The optimal location method is selected for different types of branches to achieve precise location of single-phase grounding faults in distribution networks. Simulation results show that this method has high accuracy in fault location and can achieve precise location of single-phase grounding faults in distribution networks without the need for traveling-wave detection devices across the entire distribution network.