The grounding transformer in a substation not only provides a neutral point for the medium-voltage ungrounded system, but also serves as a station for normal operation of the substation. Thus ensuring the reliable operation of the grounding transformer is essential to the safety and stability of the power system. There is a problem of the high frequency of single-phase grounding faults in the distribution lines of substations and the greater impact on the operational status and monitoring of grounding transformers. This paper analyzes the influencing factors of single-phase grounding faults on the operational characteristics of grounding transformers. A simulation model is established in the PSCAD software combined with the actual parameters of the distribution network. The correctness of the model is verified by comparing the simulated value of the zero sequence current with the calculated value of the capacitive current during a single-phase ground fault. The operating characteristics of the grounding transformer under the single-phase grounding fault are simulated and analyzed. The results show that when a single-phase grounding fault occurs, the primary side current of the grounding transformer increases and the phase is the same, but it cannot affect its safe and stable operation. During the arcing and stable grounding stages of a single-phase grounding fault, the initial phase angle of the fault, the transition resistance and the degree of detuning affect the primary voltage and current amplitude of the grounding transformer. In the stable grounding phase, the initial phase angle of the fault affects the time when the primary voltage and current are in a steady state; in the arc extinguishing phase, only the degree of detuning will affect the oscillation recovery process of the primary voltage and current. This work is supported by the National “Thirteen Five-Year” Key Research & Development Program of China (No. 2016YFB0901303).