Boehmite was prepared efficiently by adding alditols to Al-H2O reaction crystallization in moderate condition. We demonstrate that it is the interaction between alditols and metastable intermediates that inhibits the decomposition of aluminate ions into gibbsite and favors the formation of boehmite rather than the blocking of gibbsite growth sites as reported :in the previous investigations. The analysis of the crystal formation process shows that the alditols play a role before the nucleation. The interaction simulated by density functional theory and the local hard and soft,. acids and bases theory suggests that the metastable intermediates act as soft bases, while the alditols play the role of acids in the interaction, and the higher the alditols' softness, the stronger the inhibiting effect. The configuration of the interacting metastable intermediates and alditols was also verified by the comparison of both experimental and computational Fourier transform infrared spectra.