Abstract: The spontaneous coal combustion seriously affects the safety production of coal mine, and halogenation is one of the main measures to prevent and control the spontaneous coal combustion. The prerequisite for optimizing the inhibition process and improving the inhibition effect is to master the physical and chemical inhibition mechanism of inhibitor. Therefore, it is particularly important to explore the main inhibition methods of spontaneous coal combustion by halogen inhibitor, and to determine the contribution ratio of the physical and chemical inhibition to coal seam. Based on this, a method was proposed to quantitatively identify the inhibition effect of halogen inhibitor. The representative MgCl₂ inhibitor in halogenation was selected, the ultrasonic washer was used to repeatedly rinse the inhibiting and washing coal samples to obtain the experimental and reference coal samples. The change law of index gas concentration, cross point temperature, retarding rate and active functional group of different coal samples was investigated by temperature programmed experiments and infrared spectrum experiments. The physical and chemical retarding effect of halide retarder was studied from both macro and micro perspectives. The results indicated that the gas production concentration, cross-point temperature, inhibition rate and active functional group content of the washed and inhibited coal sample were significantly lower than those of the original coal sample, but higher than those of the inhibited coal sample. This suggested that the MgCl₂ inhibitor had a synergistic effect on inhibiting the spontaneous coal combustion and possessed a dual physicochemical inhibition effect. In the initial stage of coal oxygen reaction, there was a greater physical resistance compared to chemical resistance. However, in the later stages of the reaction, the chemical resistance dominated and significantly surpassed the physical resistance. The chemical inhibition effect of MgCl₂ was reflected in that it can react with the active substances in coal to form a relatively stable substance (ROCl) and magnesium complex (Mg(OH)Cl). This transformation significantly diminished the reactivity of coal, thereby mitigated the potential risk of coal self-heating. The contribution ratios of physical and chemical effects of MgCl₂ inhibitors to Pingzhuang lignite were 56.37% and 43.63%, to Tongxin bituminous coal 57.91% and 42.09%, and to Baijigou anthracite 59.60% and 40.40%. With the increase of metamorphism degree of coal samples, the contribution ratio of physical resistance increased, and the contribution ratio of chemical resistance decreased. The chemical resistance ratio of Pingzhuang lignite was 1.08 times that of Baijigou anthracite. This paper was of great significance to the mechanism of the rich halide inhibitor and provides theoretical guidance for optimizing the fire prevention process.