<p>Previous studies have demonstrated that moisture content is a key factor affecting coal spontaneous combustion (CSC), as water influences the oxidation and temperature rise of coal through both physical and chemical effects. However, existing research remains unclear on the participation degree of water in coal oxidation, reaction types, and pathways. There is a lack of systematic exploration of the reaction mechanisms of hydrogen in water during CSC, and few studies have discussed the quantitative relationship between hydrogen-containing products and moisture content. In this study, low-temperature oxidation experiments were conducted on four coal samples with varying moisture levels to examine the generation of H₂, CH₄, and water containing hydrogen during spontaneous coal combustion. This was done using thermogravimetric mass spectrometry in combination with hydrogen isotope labeling technology. Quantum chemical simulations were then employed to verify the reaction pathways at the critical moisture content. The results showed that hydrogen atoms in water made significant contributions to the formation of H₂, CH₄, product water, aldehyde compounds, and peroxides during coal oxidation at 30–220&#xa0;°C. The contribution ratios were 8.94–20.14%, 1.75–20.85%, and 8.3–35.09%, respectively. Within a specific range, an increase in the level of moisture found in samples of coal enhanced the participation of water in the formation of hydrogen-bearing compounds. However, when the moisture content surpassed a certain threshold, the participation of water in the generation of hydrogen-containing products decreased. The critical moisture content for the coal sample from Shanxi was found to be 8.2%, at which the water content contributed most significantly to the formation of various hydrogen-containing products.</p>