The invention provides a preparation method of an anode active material, which comprises the steps of: a, adding a titanium source and an organic carbon source in an organic solution with the pH value of 0-6 to prepare a mixture solution; b, adding an oxidizing agent in the mixture solution, reacting for 1-24h at a temperature of 20-80 DEG C, then separating and settling, washing with water, drying to obtain a titanium-containing precursor; and c, carrying out mixing and ball-milling on the titanium-containing precursor obtained in the step b and a lithium source, and then roasting in an inert gas. A lithium titanate composite material prepared by adopting the method disclosed by the invention has less impurity phases; the prepared nanometer lithium titanate particles are attractive in appearance; and the preparation method has the advantages of short time, low energy consumption, low cost, high yield, uniform particles of the prepared material, stable performance of the prepared material, simple and controllable process, and capability of realizing massive industrialized clean production.