The Ho³ /Pr³ co-doped NaYF₄single crystals with various Pr³ concentrations and constant Ho³ molar percentage of ~1% were grown by an improved Bridgman method. Compared with the Ho³ single-doped NaYF₄crystal, an obviously enhanced emission band at 2.85 μm is observed under 640 nm excitation. The Judd-Ofelt strength parameters (Ω₂, Ω₄and Ω₆) are calculated, the radiative transition probabilities (A), the fluorescence branching ratios (β) and the radiative lifetime (τrad) are obtained in the meantime. The energy transfer from Pr³ to Ho³ and the optimum fluorescence emission of Ho³ ions around 2.85 μm are investigated. Moreover, the maximum emission cross section of above samples at 2.85 μm is calculated to be 0.72×10^-20cm²for the NaYF₄single crystal with Ho³ molar percentage of 1% and Pr³ molar percentage of 0.5% according to the measured absorption spectrum. All results suggest that the Ho³ /Pr³ co-doped NaYF₄single crystal may have potential applications in mid-infrared lasers.