Abstract: The structural properties of N-[3-(Trimethoxysilyl)propyl] ethylenediamine (DA)-Lauroyl Chloricle (LA) (DA-LA) dual composite self-assembled monolayers (SAMs), which was prepared on silicon (Si) substrates, were investigated by molecular dynamics simulation. The optimal coverage rate and arrangement of DA and LA molecules were obtained. The wetting process of water droplet on the surface of DA-LA dual composite SAMs was further discussed, and the wetting mechanism was analyzed by contact angle and radial distribution function. The investigation shows that the system energy is lowest when the coverage rate of DA on Si surface is 50% and the coverage rate of LA bond DA is 100%. In the lowest energy system, molecules of DA-LA dual composite SAMs on Si surface are arranged orderly, it reveals the formation mechanism of dense SAMs on Si surface by molecular method. The wetting mechanism simulation was analyzed in the optimal coverage rate system. The contact angles of water droplets on the DA-LA dual composite SAMs surface are similar to the experiment results, and the surface shows good hydrophobicity. Meanwhile, the contact angles of water droplet on the DA SAM are lower than the experiment results, because the DA coverage rate is low and the chain is short, and the hydrophilic hydroxyl molecules are exposed to the upper layer. By means of measuring and calculating, the surface free energy of hydroxylated Si is highest, followed by DA surface, and the surface of DA-LA is lowest. Further analysis shows that the hydrogen bond exists between the hydroxy Si surface, DA SAM surface and the water droplet, which strengthens the surface hydrophilicity; however, the weak van Edward force exists between the DA-LA dual composite SAMs surface and the water droplet, which enhances the surface hydrophobicity.