To further study the effect of ammonium dihydrogen phosphate powder (NH4H2P2O4) on methane explosion, a quartz tube test system with a length of 1400 mm and a 20 L spherical experimental system were employed to test the flame propagation and explosion characteristics of methane-ammonia-air mixtures. The mechanisms of the reaction processes were calculated using the Gaussian 03 quantum chemistry software. The results showed that NH3 played a key role in the process of methane explosion. The addition of ammonia reduced both the upper and lower gas explosion limits, diminishing the range of explosion limits and mitigating the risk of explosion. Ammonia weakened methane explosion, and the more ammonia that was added, the more effective the weakening effect. This weakening of explosions was more efficacious for higher concentrations of methane than it was for lower concentrations of methane. According to the Gaussian calculation results, ammonia and amino groups more readily consumed oxygen and hydro and hydroxyl free radicals compared with methane and methyl groups. These consumptions caused a positive microcirculation feedback loop, which greatly reduced the quantity of methyl radicals and formaldehyde, thereby interrupting the chain reaction during methane explosion. (C) 2017 Elsevier Ltd. All rights reserved.