Abstract: In this paper, we continue to build an ultra-high speed laser schlieren testing system on the self-developed mesoscale explosion pipeline to explore the flame propagation characteristics of nitrogen and carbon dioxide inhibiting gas/air premixed gas deflagration under different injection positions and pressures. The results show that: in the experiment of inert gas inhibiting gas/air premixed gas deflagration, with the gradual increase of injection pressure, the flame propagation speed shows a trend of first increasing and then decreasing, the flame shape also gradually stretches and deforms from fingertip shape, and the middle protruding part becomes smaller until it is nearly flat; the maximum flame propagation speed of CO₂ injection near the ignition end is 20.79% lower than that of N₂ injection far away from the ignition end, and 20.25% lower than that of N₂ injection; when CO₂ is injected far from the ignition end, the minimum flame speed is 9.68% lower than that of CO₂ injection, and 12.86% lower than that of N₂ injection; compared with the two kinds of flame retarding and explosion inhibition gases, the highest flame propagation speed of CO₂ sprayed near the ignition end is 21.78% lower than that of N₂, and the lowest flame propagation speed is 1.82% lower than that of N₂. The highest flame velocity and the lowest flame velocity are 21.25% and 5.27% lower than N₂ when CO₂ is sprayed at the far ignition end.