The invention discloses a nano material for tumor imaging and treatment and a preparation method of the nano material. The nano material, which has functions of magnetic targeting, magnetic resonance imaging (MRI), up-conversion luminescence and photothermal therapy and is capable of achieving integrated diagnosis and treatment of tumors, is prepared by the following steps: firstly, preparing Fe3O4 nanocrystal by virtue of a thermal cracking process; then, on the basis of a self-assembling process, preparing a hollow polymer shell nanosphere which has a cavity and contains the Fe3O4 nanocrystal therein, carbonizing the shell and loading an up-conversion luminescence nanoparticle layer on the surface of the carbon shell by virtue of a solvent evaporation method; and finally, conducting surface modification by virtue of PEG (polyethylene glycol). The nano material, which is of a shell-core structure, comprises an external shell layer and an internal core; the external shell layer comprises the carbonized polymer shell layer; the up-conversion luminescence nanoparticle (UCNPs) layer is additionally attached to the carbonized polymer shell layer; the up-conversion luminescence nanoparticle layer is subjected to mPEG surface modification; and the internal core is Fe3O4 nanocrystal which is uniformly dispersed in the internal cavity and is superparamagnetic.