Abstract: To research the influence of moisture on the oxidation characteristics of coal, the coal spontaneous combustion experiment was carried out to determine the composite index gas that can predict the spontaneous combustion of coal, and then the temperature-programing experiments were carried out to test the changes of composite gas index during the oxidation process of coal samples with different moisture content, the change law of the composite gas index generated under the influence of moisture was researched, and the influence law and mechanism of coal sample moisture content on coal oxidation characteristics were discussed. The results of research show that the spontaneous combustion temperature of coal has an obvious relationship with CO/CH₄, C₂H₆/CO, CO/CO₂ and Graham index. The influence moisture content on the temperature rise process of coal oxidation presents different stage characteristics at different temperatures: at 30−120 ℃, moisture has both catalytic and inhibitory effects on the coal oxidation reaction, and the inhibitory effect is dominant, showing the moisture content with the best inhibitory effect is 20%; at 120−140 ℃, the inhibitory effect of moisture on coal oxidation reaction is reduced, and moisture participates in the coal oxidation reaction as a reactant, and then shows the promotion effect of moisture on coal oxidation. At this time, the moisture in the coal oxidation reaction is mainly chemically promoted, and the moisture content with the best promotion effect is 10%; at 120−140 ℃, the original pore volume of the coal sample increases due to the evaporation of water and new coal samples are produced. The tiny pores become more conducive to the occurrence of coal oxidation reaction, and then show an indirect promotion effect on the reaction. The moisture content with the best promotion effect is 15%. It was finally determined that under the influence of moisture, the composite index gas that can more accurately predict the spontaneous combustion of coal are CO/CH₄, C₂H₆/CO and Graham index. The research results can enrich the parameters of actual coal spontaneous combustion on site, increase the mining safety of high-humidity coal seams and the accuracy of spontaneous combustion prediction, and effectively reduce and prevent the occurrence of coal spontaneous combustion accidents.