In most mines, methane gas is accumulated in pores inside coal, the highest amount of which is found in coal mines, and methane is the most important polluting gas in underground coal mines. In coal mining operations, coalbed methane is one of the potential hazards that must be extracted to prevent an explosion of the accumulated gas and environmental pollution. One of the mechanisms is using microwave irradiation so that the thermal stress caused by microwave heating generates fractures. In this research, we investigated the most important parameters affecting the electric and thermal fields’ distribution in coal in order to identify the effective parameters that achieve the highest temperature increase rate and to reach the highest impact and efficiency of the system with the least amount of consumed energy. The results of this study show that the most effective parameter on the electric and thermal fields’ distribution within coal is the size of the resonance chamber.