The invention discloses a neutral point arc suppression coil grounded system single-phase grounding fault line selection method. According to a grounding fault line finding method of using bus line separation to determine the grounding fault bus system specified by an electric accident handling regulation, the bus line separation operation is performed after the single phase grinding fault of a neutral point arc suppression coil grounded system occurs, and the change features of Mi before and after the bus line separation are used for forming the line separation basis so as to achieve the reliable line selection goal. The system structurally comprises a bus of a protected power distribution system; the bus is in a single bus segmented system; a bus segmented switch uses as circuit breaker;the circuit breaker is connected with a tested control device. The test control device is connected with the voltage transformer; the voltage transformer is connected with the bus; the test and control device detects whether the neutral point arc suppression coil grounded system generates the single-phase grounding fault or not, and realizes the bus line separation operation by controlling the switching-off of the circuit breaker.