To investigate the influence of ammonia admixture on methane explosion propagation characteristics in tunneling tunnels, the explosive behavior of methane/ammonia/air mixtures was systematically examined under varying ammonia blending ratios, initial pressures, and initial temperatures. The explosion overpressure evolution and flame propagation characteristics of the mixtures under varying ammonia blending ratios, initial pressures, and initial temperatures. Results indicate that the incorporation of ammonia exhibits a dual effect on the explosion behavior: initial suppression followed by enhancement. The explosion overpressure is observed to decrease first and then increase with rising ammonia content, while the flame front position and propagation velocity progressively increase with higher ammonia ratios. Regarding the influence of initial pressure, the peak explosion overpressure, flame propagation velocity, and flame position all show linear increasing trends with elevated initial pressure. The influence of initial temperature on explosion characteristics is more complex. Within the range of 300-700 K, the explosion overpressure increases with temperature, and the flame propagation trajectory show a significant positive correlation with temperature. However, when the temperature reaches 900 K, flame propagation is markedly suppressed and manifested by significant decreases in both the flame front position and velocity. The study reveals that the ammonia blending ratio exerts a non-monotonic influence on the methane explosion process, while initial pressure and temperature regulate explosion intensity and flame propagation behavior in linear and nonlinear ways, respectively.