In this study, the 27 Al NMR chemical shifts and relative stabilities of monomeric Al 3+ hydrolytic species with different coordination structures in aqueous solution are systematically investigated by using the density functional theory quantum chemical cluster model (DFT-CM) at the B3LYP/6-311+G(d,p) level. The main work includes: the static configurations of 20 possible existing monomeric Al 3+ hydrolytic species from Al 3+ to Al(OH) 4 − are optimized, and their 27 Al NMR shieldings are calculated; the dehydration reaction pathways for typical monomeric Al 3+ hydrolytic species are modeled, and the dominant forms of the intermediate hydrolytic species of Al(OH) 2+ , Al(OH) 2 + , and Al(OH) 3 0 are analyzed based on the Gibbs free energy changes of the dehydration reactions. The important role of the tetracoordinated Al(H 2 O)-(OH) 3 0 in the formation mechanism of the polynuclear Keggin-Al 13 is discussed. This work provides valuable references for further studying the formation and transformation mechanisms of the aqueous monomeric and polymeric Al species.