The invention relates to a method for preparing lanthanum coated titanium dioxide, and belongs to the technical field of the preparation of titanium dioxide. A method for preparing lanthanum coated titanium dioxide with a uniform thin film is provided. The method includes the following steps: A, taking rutile titanium dioxide, and adding water to form slurry; B, adding iso-tridecanol polyoxyethylene ether and sodium hexametaphosphate into the slurry for dispersion by stirring to obtain a dispersion solution; C, adding a certain amount of lanthanum nitrate solution into the dispersion solution, and stirring for 20-40min; and D, adding the lanthanum nitrate solution with the same amount of that of the lanthanum nitrate solution in the step C into slurry obtained after stirring of the step C, adjusting the pH value to 8-9, mixing evenly, aging at room temperature for 20-40min, filtering, washing the solid and drying to obtain the lanthanum coated titanium dioxide. The method has the advantages of being simple and easy to realize, the obtained coating layer is uniform and stable, the hiding power and the dispersibility of the rutile titanium dioxide can be improved, and the comprehensive practical performance of the product can be finally improved.