The invention provides a three-metal-center Schiff base-aluminium compound, which has a structure as shown in the formula (I). By using triacetyl-m-trihydroxybenzene as the core, a three-metal active center binding site is provided to form three-metal-center Schiff base. On one hand, there is a large molecular space to obtain large steric hindrance. Thus, selectivity to ring-opening polymerization of lactide is enhanced, and regularity of the space structure of a polymerization product is raised. On the other hand, the three-metal-center special structure obviously enhances reaction activity of a catalyst and raises speed of a polymerization reaction. Thus, the Schiff base-aluminium compound provided by the invention has high catalytic activity and structural selectivity to ring-opening polymerisation of lactide, and regularity of the space structure of polylactic acid is raised. It shows through experimental results that the three-metal-center Schiff base-aluminium compound is used for preparation of polylactic acid, reaction yield can reach 95% and stereo-regularity (Pm) of polylactic acid can reach 0.98.