The invention discloses a nafion polymer-based Er<3+>/Yb<3+> codoped calcium fluoride nanocrystal composite material and a preparation method thereof. The preparation method is carried out according to the following steps: a nafion concentrate is prepared; Er<3+>/Yb<3+> codoped calcium fluoride nanocrystals are prepared; and the nafion polymer-based Er<3+>/Yb<3+> codoped calcium fluoride nanocrystal composite material is prepared. According to the invention, a two-step method is adopted to synthesize the composite material of the Er<3+>/Yb<3+> codoped calcium fluoride nanocrystals and nafion,which has high near-infrared luminescence, the prepared composite material film is uniform and transparent, the crystal phase structure of the nanocrystals in the composite material is a cubic crystalphase, the nanocrystals are single-phase crystals, and the nanocrystals have uniform grain size and good dispersibility, and do not have an obvious agglomeration phenomenon. The preparation method disclosed by the invention is simple and easy to scale up, the controllability is good, the properties of the product are excellent, and therefore the composite material and the preparation method havea broad market prospect.