Tm³⁺ doped LiYF_4single crystal in size of Φ 10mm×110mm with high quality was grown by the Bridgman method.The XRD,absorption spectrum,and emission spectrum of the sample under 790nm excitation are measured.The intensity parameters (Ω_t ),oscillator strength (P_exp),transitio n probabilities(A),branching rations(β) and radiation lifetime (τr ad) of Tm³⁺ ions in the LiYF_4were estimated by using the Judd-Ofelt theory. The absorption and emission cross sections around 1800nm were calculat ed to be 0.52×10－20cm^2and 0.67×10－20 cm²,respectively.The emission bands are 1470nm and 1800nm,which are corresponding to 3H₄→³F₄and ³F₄→³H₆transitions of Tm³⁺ ion.The emission lifetime at 1800nm is recorded,and the quantum efficiency is calculated to be 79.22%.