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Pure hexagonal β -NaYF4 micron crystals were synthesized by the hydrothermal method with the up-conversion luminescence properties studied by doping Yb 3 + /Ho 3 + . The up-conversion fluorescence spectra and fluorescence lifetime of β -NaYF4 micron crystals were determined by FLS-980 transient fluorescence spectrometer. By changing the doping concentration of Yb 3 + /Ho 3 + , the optimal doping concentration was confirmed to be 20%Yb 3 + /2%Ho 3 + . The fluorescence spectrum was obtained by changing pump power, the relationship between power and intensity was analyzed, and the β -NaYF4 micron crystal green and red emission up-conversion process was obtained into a two-photon process. The 5F 4 → 5 I8 and 5S 2 → 5 I8 of the sample were thermally coupled to obtain a large absolute sensitivity (Sa) of low temperature. The maximum absolute sensitivity within the range of 64–194 K is 0.0097 K − 1 at 144 K, while maximum absolute sensitivity at 333 K is 0.00335 K − 1 in the range of 293–493 K. The experimental results show that the sensing characteristics of β -NaYF4:Yb 3 + /Ho 3 + at low temperature are better than those at high temperature, and it has the potential to be used in the field of temperature sensing. [ABSTRACT FROM AUTHOR]