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Gas explosion accidents are a leading cause of casualties in underground coal mines. This study investigates the variation patterns of explosion temperature and pressure under different initial gas concentration conditions using a 20 L explosion characteristic test system and high-precision sensors. Accurate post-explosion gas analyses were conducted using a GC9560 gas chromatograph. Our research aligns with global research, finding that initial gas concentrations within the range of 5.8%–13.3% generate maximum explosion pressures between 0.3 and 0.9 MPa, posing a significant overpressure hazard to humans. Comprehensive fitting analyses of various post-explosion gases reveal that at an initial gas concentration of 10.6%, the produced H2 can reach its lower explosion limit, indicating a risk of secondary explosions. Furthermore, post-explosion CO levels can peak at 9.87%, potentially causing poisoning or death, while elevated CO2 levels and diminished O2 concentrations could lead to asphyxiation. A unique observation at a 9.5% concentration was a secondary temperature rise, with the relationship between temperature delay, heating time, and initial gas concentration presenting a U-shaped pattern that mirrors theoretical expectations. This study advances the field by addressing research gaps in post-explosion gas analysis and emphasizing the necessity of precise monitoring and control of gas concentrations, thereby offering novel insights and substantial theoretical and practical contributions to the prevention of gas explosion incidents in underground coal mines.