Abstract: For the problem of single-phase grounding fault line selection in neutral point ungrounded systems, this paper proposes a transient steady-state fusion fault line selection method based on wavelet support vector machine. Firstly, the single-phase grounding fault mechanism of the neutral point ungrounded system was analyzed, and a fault line selection basis including steady-state characteristics and transient components was constructed. At the same time, wavelet decomposition technology is used to extract the time-frequency characteristics of the initial zero sequence current of the fault, obtain key parameters such as transient energy distribution and signal complexity, and fuse transient and steady-state features to form a high-dimensional feature vector, which is input into the support vector machine classification model for intelligent identification of the fault line. Through simulation platform verification, the line selection performance under different fault conditions was demonstrated, and the influence of factors such as fault resistance and transition resistance on line selection accuracy was explained. The results indicate that this method significantly improves the accuracy of line selection and environmental adaptability, providing an effective solution for fault line selection in neutral ungrounded systems.