Abstract: Anionic surfactant (SDS) was used to modify the coal to improve coal seam wettability,reduce the compactness of the coal structure,and reduce or avoid gas accidents.Fuxin Long flame coals were taking as the research object.The contact angle experiment and uniaxial compression experiments were carried out to determine the macrophysical and mechanical properties (such as contact angle,peak strength,peak strain and elastic modulus) of the coal sample after modification with different conditions.X-ray diffraction and Fourier infrared spectroscopy experiments were used to determine the changes of micro structure (such as mineral composition and surface functional groups) in the coal sample after modification with different conditions.The quantum chemical density functional theory was adopted to explore the modification of coal by surfactants,and to analyze the structure damage process of coal after SDS modification.The results show that when the mass concentration of SDS solution was 0.5%,the modification time was 48 h,and the modification temperature was 40 ℃,the contact angle of coal was the smallest,the peak strength and elastic modulus de-creased the most,and the peak strain increased the most.After the SDS solution was modified,the content of carbonate minerals in the coal sample decreased,and the content of silicate minerals increased.The micro crystalline structure integrity of coal was poor,the functional groups and various bridge bonds in coal mole-cules were rich,especially the fat functional groups were more,and the ordering order was lower.Based on the quantum chemical density functional theory,the modification of surfactant on coal was explored.In other words,the surfactant was adsorbed on the coal by electrostatic force,and the functional groups and chemical bonds of the organic minerals in the coal were broken,and some inorganic minerals were dissolved and dis-persed.This was also the main cause of damage to the coal structure.The chemical reaction on the coal surface produced secondary pores and fissures,these secondary pores and fissures were interconnected to form cracks.With different modification conditions,the cracks continued to extend until the cracks penetrating the entire coal,which led to the overall coal structure damage,and the mechanical strength of coal continued to decrease.