The invention discloses a preparation method of nano lithium titanate and relates to the field of preparation of nano materials. The method comprises the steps of firstly preparing a suspension from Ti2AlC ultrafine powder and a lithium hydroxide water solution, and carrying out hydrothermal reaction to obtain mud sediment; re-dissolving the mud sediment and then removing the sediment to obtain a gel solution; and filtering the gel solution to obtain nano lithium titanate precursor powder and then calcining to obtain crystalline nano lithium titanate powder. The nano lithium titanate prepared by the technological processes is superfine nanoparticles and is good in dispersity; and a product contains a little of evenly distributed carbon with good conductivity. The invention further provides a preparation method of a negative electrode material for a battery. The negative electrode material for the battery is prepared by using the preparation method of the nano lithium titanate. The product is a carbon-doped nano lithium titanate with high dispersity, is uniform in carbon distribution and is the negative electrode material for a lithium-ion battery with high capacity and good rate capability.