Abstract: In recent years, magnesium hydroxide has been one of the most widely used flame retardant materials, but its products still have shortcomings, such as high surface polarity, ease of reunion and difficulty in compatibility with polymer materials. In this paper, the adsorption of oleic acid, silane coupling agent G-570 (γ-methacryloxy propyl trimethoxysilane) and methyl methacrylate (MMA) on the surface of magnesium hydroxide (101) was simulated by density functional theory (DFT), and the modification mechanism on the surface of magnesium hydroxide was studied. The results were analyzed by adsorption energy, the density of states, differential charge density and Mullikan population charge. The results show that oleic acid has the lowest adsorption energy among the three modifier molecules and can be stably adsorbed on the magnesium hydroxide (101) surface. After adsorption, there is obvious charge transfer between oleic acid and the magnesium hydroxide (101) surface, forming Mg-O interactions, which is the key to the surface modification of magnesium hydroxide. The research results of this paper provide useful theoretical guidance for improving the properties of magnesium hydroxide flame retardant materials.