Er3+/Yb3+ ion co-doped fluoride particles are synthesized and analyzed by their absorption spectra. The influence of the substances, the calcination temperature, and the doping ratio of Er3+ and Yb3+ on the absorption of the synthesized materials are studied. By analyzing the spectra of the samples with the Judd-Ofelt (J-O) theory, the intensity parameters are obtained as Ω2=9.9887, Ω4=2.7333, Ω6=0.4868, respectively. The results show that the phonon assisted transition probability and the energy transfer efficiency increases after heat treatment of the samples. The best doping ratio of Er3+ and Yb3+ is 16. Analysis based on the Judd-Ofelt theory shows that the synthesized fluoride particles have low phonon energy and good absorption property in the near-infrared region after doping with Er3+ and Yb3+ ions. It can be used as a kind of good materials for near-infrared upconversion.