It is important to realize fault line selection, transition resistance measurement and fault property determination in the process of flexible arc suppression for single-phase grounding fault detection in the existing distribution network. Considering a flexible grounding system with asymmetric three-phase ground parameters in a distribution network, first, the influence of unbalanced zero-sequence voltage on arc suppression effect is analyzed, and a calculation method of full compensation current for flexible arc suppression is proposed. Then, the constraint relationship between the injected current and the bus zero-sequence voltage in normal operation and in single-phase grounding fault is analyzed. The results show that no matter what state the system is in, the bus zero-sequence voltage can be flexibly regulated by changing the injected current, and then the zero-sequence current of each line can be regulated. According to the variation law of zero-sequence current of each line before and after flexible regulation of zero-sequence voltage, a fault detection method that can realize fault line selection, transition resistance measurement and fault property determination is proposed. The effectiveness and accuracy of the method are verified by Matlab/Simulink simulation.