Abstract: This paper describes the electrical discharge characteristics in the optical cavity of a high-power KrF excimer laser amplifer operating as an oscilator. Several factors in connection with the output of laser energy have been studied. For the first time in China we successfully achieved a large volume(85cm × 3cm × 1.3cm) uniform KrF discharge with more than 130mJ laser output energy for a single pulse. In addition, detailed experimental results are presented here and further discussion and analysis on the related physical mechanism are presented.