Yb3þ/Tm3þ and Yb3þ/Er3þ co-doped NaLuF4 crystals were synthesized by a facile hydrothermal method. The optical temperature sensing properties of Tm3þ based upon its two thermally coupled energy levels 3F2, 3 and 3H4 were systematically investigated by means of fluorescence intensity ratio (FIR) technique. The 980 nm laser-induced thermal effect on Tm3þ doped NaLuF4 crystals was studied by using Er3þ doped sample as thermal probe. The temperature sensitivity of Tm3þ in NaLuF4: Yb3þ/Tm3þ crystals shows a nonlinear dependence on temperature, and the maximum value is about 0.00045 K『1 at 600 K. The accuracy and reliability of the optical thermometry based on Tm3þ in NaLuF4: Yb3þ/Tm3þ crystals has been checked by using Yb3þ/Er3þ co-doped sample as temperature sensing unit. The results demonstrate that NaLuF4: Yb3þ/Tm3þ crystals have good sensing stability and may have potential application for the optical thermometry.