Abstract: We studied reducing laser bandwidth by intracavity etalons,and discussed severalfactors which would affnect the experimental result.We did the experiment research on a dischargepumped,long pulsc duration KrF excimer laser, in which three etalons provided spectraldispersion,In the experiments,we studied the influence of the apertures and the rate of outputput coupling.Selecting suitable paramters,we got output linewidth no more than 3GHz,thisvalueis 1 000 times smaller than the linewidth when free running.