Abstract: Output characteristics were tested under two diluent injecting methods on a single tube discharge excited infrared multi-band chemical laser by taking DF as a typical case. Experiment results of laser power output, mode characteristics, and spectra distributions indicated that injecting He from the end of discharge tube in addition to regular He injecting can increase the power of output, lengthen flow direction's gain length and strengthen the transitions between higher vibration levels, the reason was attributed to reduction of combination less of F atoms on wall, increase of active zone's flow rate and mitigation of deactivation effect.