A study of the temperature dependence on an absorption coefficient is presented. We describe the absorption spectrum measurement of the laser material Yb:YAG that was performed over a wide temperature range. As the temperature increases from $23°\mathrm{C}\text{to}300°\mathrm{C}$ , the central wavelength of the Yb:YAG absorption spectrum at $940\mathrm{nm}$ varies slightly from $941.2\mathrm{nm}\text{to}941.1\mathrm{nm}$ , and the maximal absorption cross section drops dramatically from $7.89\times {10}^{-21}{\mathrm{cm}}^2\text{to}4.23\times {10}^{-21}{\mathrm{cm}}^2$ . According to our experimental results, we have presented an analytic description of temperature distribution with the numerical iterative method and have investigated the pumping optimization and laser oscillator performance, taking into account that the absorption coefficient is strongly influenced by temperature. Our analyses also include the effect of pump absorption saturation and the temperature dependence of Boltzmann population fractions, stimulated emission cross section, and thermal conductivity. We have shown that the predicted laser output power exceeds the actual value if the temperature dependence of Yb:YAG’s absorption coefficient is neglected.