Er3+/Yb3+ co-doped TeO2-ZnO-La2O3 glasses were prepared, and the absorption spectra, fluorescence spectra and upconversion emission spectra of Er3+ ions were measured. Effects of Yb3+ on the infrared fluorescence at 1.5 μm band and the visible upconversion luminescence of Er3+ in the glasses were investigated under the excitation at 975 nm. With the increase of Yb2O3 concentration, the 1.5 μm band infrared fluorescence intensity and the visible upconversion luminescent intensity increase evidently due to the effective energy transfer from Yb3+ to Er3+, but the latter increases more efficiently. According to the simulation of rate equations, the theoretical result agrees well with the experiment, indicating that Er3+/Yb3+ co-doped tellurite-based glass is a promising gain media suitable for developing upconversion fiber lasers. And the analysis to upconversion emission shows that a two-photon upconversion process is assigned to the intense green and red emission, respectively.