The invention relates to the technical field of power system relay protection, in particular to a single-segmented-bus parallel-PT logic judgment method for selecting a line with a small grounding current. According to the method, information of a section switch and information of PT switch node signals are collected in real time, and real-time switching is achieved for the PT signal of the section I and the PT signal of the section II by analyzing the logic relation between the section switch and the PT switch nodes. The method is beneficial for improving accuracy and reliability of line selection.