The invention discloses an organic electroluminescent nano composite material which is a solution-processible core-shell structure constructed by taking a small-molecule electroluminescent material as the core and conductive polyaniline as the shell, wherein the small-molecule electroluminescent material is selected from aromatic ring compounds (such as benzene, naphthalene, fluorene and the like) and derivatives thereof. The preparation method of the organic electroluminescent nano composite material comprises the following steps: preparing a surfactant solution; then taking a part of surfactant solution, and dissolving ammonium persulfate therein, thus obtaining a solution A; dissolving an aniline monomer and the small-molecule electroluminescent material in the residual surfactant solution, thus obtaining a solution B; stirring the solution B in a thermostatic water bath; dropwisely adding the solution B into the solution A, and further stirring the mixed solution after the dropwise addition is finished; and adding demulsifier into the mixed solution, demulsifying, performing vacuum filtration, performing vacuum drying to obtain the organic electroluminescent nano composite material. The organic electroluminescent nano composite material can be applied to an organic electroluminescent device.