Abstract: Coal seam water injection can effectively inhibit gas gushing in the process of coal mining, and its inhibition effect mainly depends on the wetting characteristics of coal seam. The chemical structure of coal is one of the important factors affecting the wettability of coal. In order to study the relationship between the functional groups of medium and low rank coal and its wettability, the coal quality characteristics of typical medium and low rank coal samples were analyzed, and the parameters of different coal samples were obtained by Nicolet iN10 Fourier Transform microscopic infrared spectrometer. In this paper, the size of the contact Angle of deionized water at the solid-liquid-gas junction on the coal surface is used to characterize the wettability of coal. JC2000D contact Angle measuring instrument is used to obtain the contact Angle of different coal samples. Zeta potential can reflect wettability and ionization degree of coal surface functional groups, so as to establish the relationship between hydrophilic functional groups (hydroxyl functional groups, other oxygen-containing functional groups), contact Angle and Zeta potential of coal samples. The experimental results show that with the deepening of coal metamorphism, the strength of hydrophilic functional groups of coal samples decreases gradually, the peak height of hydrophilic functional groups of middle rank coal decreases by 0.13 compared with that of low rank coal, and the absorption peak area decreases by 58.91. The hydrophilic functional groups are negatively correlated with the contact Angle of coal samples, that is, the contact Angle decreases gradually with the increase of absorption peak intensity of hydrophilic functional groups, and the contact Angle decreases by 8.27 ° from middle rank coal samples to low rank coal samples. The relationship between hydrophilic functional groups and Zeta potential of coal samples shows a first-order exponential decay function, and the correlation coefficient is as high as 0.95. That is to say, the absolute value of Zeta potential increases gradually with the increase of absorption peak area of hydrophilic functional groups. The surface electronicity of coal samples is strong, and the hydrophilicity of coal is good. Among them, the hydroxyl functional group has a great influence on the wettability of coal, and the hydrogen bond formed by self-associating hydroxyl group is the main factor affecting the wettability of coal. Other oxygen-containing functional groups, such as carboxyl and ether bond hydrophilic functional groups, combine with water molecules under intermolecular force, showing strong vitality and improving the hydrophilicity of coal.