The invention belongs to a nano-radiography material, in particular to a preparation method and application of trimanganese tetroxide nano-radiography material with target function. The current radiography material has the defects that tumour is detected through the magnetism performance of the material, the target function is not available, and the radiography material can not accurately enter tumour cells, therefore, normal tissues can not be distinguished from the tumour tissues. The preparation method of the trimanganese tetroxide nano-radiography material with the target function comprises the following steps: firstly, preparing monodisperse, water soluble and amino functionalized magnetic nano-material which has a trimanganese tetroxide/silicon dioxide core shell structure; secondly, quantificationally detecting the amount of amido on the surfaces of nanoparticles by using an amido density testing method; and thirdly, preparing the trimanganese tetroxide nano-radiography material with the target function by fixing the proportion of the quantity of organic fluorescein and folacin target molecules connected on the surfaces of the nanoparticles. The invention has the advantagesthat the equipment is simple, and the preparation is easy; the nano-radiography material has fluorescence, magnetism and target function; and the radiography material has uniform grain diameter, gooddispersity and water solubility and magneto-optical double functions.