The invention belongs to the field of inorganic nonmetallic material preparation, and particularly relates to a preparation method of a lanthanum titanate nanometer material. The preparation method comprises the steps that lanthanum nitrate, titanium acetylacetonate and citric acid are taken as raw materials, the raw materials are stirred to be dissolved in water and then subjected to a cross-linking reaction under the stirring and heating conditions, a reaction product is naturally cooled and then put into a mortar to be ground, a continuous high-temperature calcining reaction is conducted, the temperature is lowered to room temperature, and then the lanthanum titanate nanometer material is obtained, wherein the mole ratio of lanthanum nitrate to titanium acetylacetonate to citric acid is 1:1:(6-60). According to the preparation method, the purity of the target product is high, and the preparation cost is low; the yield of the target product ranges from 99.2% to 99.8%, the size of the target product ranges from 30 nm to 50 nm, and the requirement on the lanthanum titanate nanometer material product in the industrial application field can be met; products made of the material can be applied to the fields of ferroelectric cells, photovoltaic cells, photocatalytic cells, fuel cells and the like.