Abstract: Using C₄F₇N gas mixture to replace SF₆ is an important way to improve the environmental friendliness of the ring main unit (RMU). In order to ensure the reliability of power supply, grounding switches in C₄F₇N gas mixture insulated RMU were experimentally investigated to optimize equipment performance and to support the engineering application. Firstly, the closing time and speed of the grounding switch in different volume ratios of C₄F₇N/CO₂ gas mixture and SF₆ were measured. It was found that it was consistent with the air, indicating that the mechanical characteristics of the grounding switch are stable and independent of the gas. Then, the pre-breakdown characteristics of grounding switch in different gases were studied, and the influence of voltage and gas type on pre-breakdown time was analyzed. The results show that the pre-breakdown time increases with the increase of voltage, and the pre-breakdown time decreases with the increase of C₄F₇N volume ratio. Furthermore, the experiments were carried out by using the built grounding swicthing experiment circuit of the RMU. It was found that increasing the volume ratio of C₄F₇N was helpful to reduce the amount of arcing charge transfer and reduce the degree of contact ablation. Combined with the liquefaction temperature and economic index of the gas, 10% C₄F₇N/CO₂ gas mixture was selected as the insulation medium of the RMU. The verification experiments reveal the switching performance can meet the standard requirements.