The invention discloses an upconvresion composite nano-material as well as a preparation method and application thereof. The nano-material is of a core-shell structure, and comprises synthetic Nd<3+>-doped 800nm laser excited nano-particles with a heating effect, an upconversion fluorescence nano-shell layer coating the outer layer, an isolating layer which can be added in the middle depending on the difference of outer layer materials, and a shell layer which is additionally arranged outside an illumination layer to intensify the illumination strength. The method for synthesizing the nano-particles is simple, easy to operate and strong in controllability, and particles with different diameters can be synthesized by controlling the usage of raw materials. The nano-particles synthesized by the method integrate the independent photothermal effect of the material and the upconversion illumination effect, and can be applied to preparation of tumor diagnosis preparations, temperature detection reagents and tumor treatment medicaments, and biological imaging.