<p>The spontaneous combustion is a typical hazard in the production, transportation and storage of coal. Particularly, low-rank coal has a higher tendency to spontaneously combust compared to high-rank coal. In this context, this study examined lignite, long-flame coal and non-caking coal, three types of low-rank coals with varying metamorphic grades, through simultaneous thermal analysis experiment. The investigation aims to comparatively analyze their oxidation characteristics and elucidate the underlying mechanisms governing their differential reactivity. Based on the thermogravimetric and derivative thermogravimetric curves, the characteristic temperatures of the three coals were determined, enabling the delineation of distinct oxidation reaction stages. Furthermore, the contributions of various parallel reaction mechanisms to the mass loss were investigated using Gaussian multimodal fitting methods. The results demonstrated that, with the advancement of metamorphic grade, the boundary temperatures and the peak temperatures corresponding to the mass change rates during the oxygen adsorption, pyrolysis and combustion stages gradually increased, the proportion of mass contribution from thermal decomposition and gas-phase combustion gradually decreased, as well as the proportion of solid-phase combustion mass contribution gradually increased. The apparent activation energies (<i>E</i>_a) of three coals during the stages of oxygen adsorption, pyrolysis and combustion were calculated using the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) model-free method. The results revealed that the <i>E</i>_a of the coals at each stage were positively correlated with the metamorphic grade, but distinct relationships were observed between <i>E</i>_a and conversion rates across various stages. During the oxygen adsorption stage, the <i>E</i>_a exhibited a monotonic increase with rising conversion rates. In contrast, during the pyrolysis and combustion stage, <i>E</i>_a initially increased but subsequently decreased as the conversion rate progressed. Based on the differential scanning calorimetry curves, the interval heat release at different temperature ranges and total heat release of coals were examined. The results demonstrated that the total heat release from coal increased with higher metamorphic grade. The lignite with the lowest metamorphic grade displayed a drastic thermal release but was limited in the high-temperature range; in contrast, the heat release of long-flame and non-caking coal with the higher metamorphic grade tended to gradual and extended to higher temperature range. This research is crucial for understanding the oxidation behavior of low-rank coal, formulating scientific and effective measures to prevent its spontaneous combustion, ensuring the safe and sustainable utilization of coal resources.</p>