Abstract: In order to study the timeliness change laws of the leading role of displacement and replacement in the process of injecting air to coal to displace and replace the methane in coal, we carried out the simulation experiment of injecting the air to displace and replace the methane in coal under the low injection press of air. The experimental results show that all the injected air has been trapped in the coal in the first 8 min after the start of the experiment, and the injected air in this stage show the displacement effect in the leading role, and the transient displacement is weak. Since then, the transient displacement has been decreasing, the instantaneous displacement effect has been increased all the time; but the instantaneous displacement remains strong in the instantaneous displacement at the early stage of the experiment, the turning point appeared in the 112 min to 122 min, the instantaneous displacement is equal to the instantaneous displacement, then instantaneous displacement effect is always stronger than instantaneous displacement. Finally, the instantaneous displacement tends to 0, and the instantaneous displacement effect is in the leading role. In the whole experiment, the cumulative effect of the injected air is 26%, and the cumulative effect of displacement is about 74%.