Reducing the diameter of the discharge tube used in the discharge driven HF/DF chemical laser is useful for integration of multi- module, and may be useful for promoting the performance of the laser as well. The glow discharge characteristics and laser operated parameters of three different discharge tubes were experimental studied, and the diameter of the discharge tubes was 28mm, 20mm and 16mm, respectively. When NF₃gas was injected, the plasma necking phenomenon occurred in all three discharge tubes. For the laser which used the 20mm diameter discharge tube, the plasma necking phenomenon was the weakest, the total consume of working gas was the least, the output power and the electro-optic transfer efficiency were the highest, and the laser output power promotion effect by secondary He was the most outstanding. Through comparison, it is suggested that the stability and volume of the plasma are two intuitionistic parameters for judging the performance of discharge tubes.