Diluent gas is one of the HF/DF chemical laser fuel gas compositions, which adjust and control combustion temperature. Different diluents affect laser output power. In this paper, firstly we investigated the power variety of chemical DF laser connected to vacuum tank which took He, Ne, Ar, N<sub>2</sub> as diluents respectively. Then we studied the absorbility of the four diluents on zeolite. The results showed that the output power of diluent gas was He>Ne>N<sub>2</sub>>Ar; the adsorbance was <<HeNe<Ar<N<sub>2</sub>. So we concluded that the N<sub>2 </sub>was the best diluent gas candidate for DF chemical laser with a cryosorption vacuum pump to adsorb the exhausted gas.