A fluid model is used to investigate the discharge kinetics of ArF excimer laser. By comparing the gas discharge at different initial preionization intensities, the effects of preionization on discharge excited excimer laser system are analyzed. The preionization effect under different gas parameters is also discussed. The results show that the initial preionization intensity has significant effects on the breakdown voltage, the formation of ArF excimer, the optical quality and gain. Under the premise of uniform electric field and effective discharge, it is difficult to reach the gas breakdown threshold with low initial preionization intensity, but higher laser power can be obtained. Increasing the initial preionization intensity can effectively reduce the breakdown voltage, but it’s not conducive to the absorption and conversion of energy. The preionization capability is affected by the gas pressure and fluorine ratio. The increasing of gas pressure or fluorine concentration can reduce the effectiveness of preionization.