An experimental study on the ignition and combustion mechanisms of a methane-air mixture in a divided constant-volume combustion chamber was conducted in this paper. The effects of the initial pressure, equivalence ratio, and orifice diameter on the mechanism pattern were studied using the pressure curve and rate of pressure rise, and the jet speed and the flame propagation speed in the lower chamber were measured. The ignition and combustion mechanisms of the methane-air mixture in a divided constant-volume combustion chamber can be classified into three patterns: (i) chemical chain ignition and burning, (ii) composite ignition and burning, and (iii) flame front ignition and burning. Reasonable explanations for each pattern were then presented. Characterization parameters were defined so that the mechanism pattern can be easily confirmed under any condition. The appropriate increase in the initial pressure, equivalence ratio, and orifice diameter were helpful in obtaining a higher burning speed. Ultimately, analyses of the jet and flame propagation speeds in the lower chamber proved that pattern (ii) was the most advantageous for increasing the burning speed.