Abstract: On the basis of a single-layer hydrotalcite model, various computations with density functional theory (DFT) were carried out for the purpose of investigating the relationship between the Al/Mg molar ratio and the stability of single-layer hydrotalcite. With the increase in the Al/Mg molar ratio, both Al—O and Mg—O distances gradually became large and reached maximum at the ratio of 7:12. But once Al—O—Al triple was formed by continuously increasing the ratio, the case was dramatically different and the hydrotalcite structure phase dissolved. In consideration of the difference of the bond energy between Al—O and Mg—O, the structures formed at Al/Mg molar ratios of 6:13 and 7:12 were much more stable among all the constructed ones. In fact, if these results are extended to single layer hydrotalcite, high symmetry structures with the ratios of 1:2 and 1:3 will be easily obtained in experiment. Therefore, in the case, where the formation of Al—O—Al triple is avoided, the best synthesizing scheme may be heightening the ratio of Al/Mg.