Abstract: Aiming at the problem that when a high-resistance grounding fault occurs in a flexible grounding system, the input of a small resistor in parallel leads to a smaller fault steady-state component and low protection sensitivity, the characteristics of zero-sequence current-voltage distribution in the faulty area and non-fault area before and after the insertion of resistance was analyzed. Based on the characteristics of transient and steady-state zero-sequence current-voltage, a quick fault handling method for single-phase ground faults suitable for flexible grounding systems was proposed. A ground fault protection device was designed to implement the proposed method. The correctness and effectiveness of the proposed method were verified by Real-Time Digital Simulation(RTDS) tests. The research improved the sensitivity of the protection system and optimized the fault handling speed.