Aiming at the problem that the correct rate of line selection decreases due to the weakening of the zero-sequence current similarity of the sound line with multi-cable resonant grounding system and the weak fault information of single-phase high-resistance grounding. A line selection method based on the symbolic aggregation approximation (SAX) and spatial information entropy is proposed. Firstly, low frequency transient zero sequence current is extracted by FIR filter and normalized, and then the low-frequency current sequence and its difference sequence are symbolized on the multi-scale domain, and the three-dimensional fault space is generated after the longest common subsequence check and the spatial information entropy is defined, and finally the entropy difference between lines is compared to complete line selection. The simulation results show that the line selection method has high sensitivity, low hardware requirements, and can overcome the difficulties of sampling asynchronization and three-phase unbalance.