Abstract: The state-of-art cost of environmental-friendly SF₆/CF₄ mixed insulating gas of GIS equipment in the power system is relatively high. In order to ensure its insulation and arc extinguishing performance, SF₆ gas is overfilled on site, which is not in line with the purpose of using the mixed gas to achieve environmental protection and prevent liquefaction. Therefore, an optimized method of timed alternate gas blending for environmental-friendly SF₆/CF₄ mixed insulating gas based on a single mass flow controller is proposed. Through the timed alternate gas blending and instant mixing technology, the gas blending error caused by residual gas in the shared gas pipeline is analyzed and optimized. The SF₆ gas output time correction technology and the time reallocation method for the last period are studied, further reducing the error in the mixing ratio of the filled gas. Simulation experiments show that the deviation of the instantaneous mixing ratio and the mixing ratio after 24 hours from the target value is less than ±0.5%, which meets the requirements of DL/T 2243—2021 standard.