In this article, beta-NaLuF4:Yb3+/Tm3+/Er3+ were synthesized by thermal decomposition technique. Yb3+/Tm3+/Er3+ has been firstly manifested to fabricate the microfibers after co-doping with polymer solution. The guiding performance of a microfiber was observed under 980 nm excitation source to prove that it could be used as an active and passive waveguides. The characteristics of optical thermal sensing of Tm3+ and Er3+ ions in a single microfiber were demonstrated. The FIR method was utilized to evaluate the sensitivity of a single microfiber and maximum sensitivity of activator ions in a microfiber was achieved as 0.00124 and 0.00311K(-1) with temperature ranging from 303 to 363 K, respectively. Our results suggest that a single microfiber has good sensing stability and has potential applications in the field of thermometry.