In order to solve the problem of poor fault line selection when single-phase grounding occurs in resonance grounding system of distribution network, a new method of fault line selection for resonance grounding system based on S-transform and reliability decision fusion is proposed in this paper. In this paper, the S-transformation powerful time-frequency analysis capability is used to extract the complex time-frequency matrix of each line, and the two criteria of the correlation coefficient and the transient energy parameter of each line frequency-frequency matrix are integrated by credibility decision, so that the fault line selection can be realized adaptively and the accuracy and sensitivity of the single line selection method can be improved. On the other hand, the paper use EMTP/ATP software to build a hybrid line simulation model of 10 kV distribution network. The simulation results show that this method can fuse a variety of characteristic variables well. It is less affected by neutral grounding mode, fault location, fault resistance, fault initial angle and network structure, and has higher criterion margin. It has higher efficiency in the case of multi-circuit and cable hybrid feeders.