With a 980nm laser diode (LD) pumped, the sensitized effect of Yb 3+ ions on 2.7μm emission properties and energy transfer mechanism in Yb 3+ /Er 3+ co-doped tungsten–tellurite glass were investigated in present paper. Based on absorption spectra, Judd–Ofelt parameters and radiative transition probabilities were calculated and analyzed. The emission spectra were tested and the optimized concentration ratio of Yb 3+ to Er 3+ ions was found to be 3:0.5 with a largest calculated emission cross-section (6.05×10 −21 cm 2 ) corresponding to Er 3+ : 4 I 11/2 → 4 I 13/2 transition. When the concentration ratio of Yb 3+ to Er 3+ ions was 4:0.5, 1.5μm and 2.7μm emission decreased while up-conversion increased. The decreased 1.5μm and 2.7μm emission were induced by the saturation of Er 3+ : 4 I 13/2 level. In brief, the advantageous spectroscopic characteristics indicated that Yb 3+ /Er 3+ co-doped tungsten–tellurite glass may be a promising candidate for application of 2.7μm emission.