In analyzing GIS equipment failures in high-altitude regions, it was discovered that winter faults accounted for 46% of total failures. This is primarily attributed to the liquefaction susceptibility of SF6 gas in environments characterized by high pressure and low temperature, posing a significant risk to the safe and stable operation of GIS/GIL equipment. To enhance the gas's resistance to liquefaction, SF6/N2 gas mixtures are commonly utilized instead of pure SF6 gas in engineering applications. However, the introduction of N2 gas can lead to a reduction in the insulation capability of GIS equipment. To investigate the influence of pressure and temperature on the gas discharge characteristics of the mixed gas, this study calculates simulation on plasma discharge of 20%SF6/80%N2 mixed gas at different temperatures and pressures, obtaining the spatiotemporal distribution of microscopic parameters changes within the mixed gas flow and the electron density, positive and negative ion concentrations, and chemical reaction rates. The results indicate that with increasing pressure, the chemical reaction rates initially rise before stabilizing, while with decreasing temperature, they exhibit a trend of increasing in the early stages of streamer development and decreasing in the intermediate and later stages. The electron density and the streamer development process follow similar trends in variation. This paper reveals the mechanism of the impact of temperature and pressure on the insulation performance of SF6/N2 mixed gas, laying a theoretical foundation for subsequent research on the adaptability of high-voltage electrical equipment to low-temperature environments.