This article introduced a method of measuring temperature which was named absorption spectrum temperature-measurement method;the relationship between the absorption coefficient and the temperature of thermal equilibrium flow field for HF/DF chemical laser was analyzed by the theory of gas absorption. Used the 1p9 and 1p8 spectral line of a discharge driving continuous wave (CW) single-line HF laser as detect light source,the transmittance of the flow field that behind the gain field of a discharge driving CW HF/DF laser was experimental measured,which changed with the flow rate of injected hydrogen gas. The flow rate of HF gas was estimated,combined with the pressure of flow field and other data,the temperature variety scope of the flow field was computed by the absorption coefficient formula. The result and error source were analyzed. This method can be used for measuring gas flow field temperature of gas flow laser and engine combustor.