As a hydrogen-rich and carbon-free fuel, ammonia is regarded as a promising carrier and storage medium for clean energy. By mixing methane with ammonia, the emission of carbon dioxide is also significantly reduced, which is of great significance for reducing greenhouse gas emissions and protecting the environment. However, ignition studies of ammonia/methane mixtures are still limited. In this paper, by means of numerical simulation with detailed chemical reaction mechanism, the effect of ammonia replacing methane on combustion was analyzed. Characteristics of explosion limit under different temperature (750-850K), equivalent ratio (0.5, 1.0 and 2.0) and ammonia mixing ratio (0-90%) were studied. The results show that the explosion limit decreases with the increase of temperature and equivalence ratio. When the proportion of NH3 is around 10%, the explosion limit shows a turning point. When the mole fraction of NH3 is higher than 50%, the explosion limit shows obvious increasing tendency with ammonia addition. Moreover, sensitivity and rate of production were also analyzed to expand the understanding of explosion limit for premixed ammonia-methane fuel blends.