Abstract: In order to obtain the homogeneity of pulse discharge at the high pressure,a X-ray preionization source for excimer lasers is introduced in this paper.The X-ray results from the impact of accelerated electrons against a Tatarget.The shorter the wavelength of X-ray is,the ability of the preionization is much stronger.With the X-ray preionization source,the preionization electrons density of 2.9×108cm-3 can be obtained in He:Xe:Fe mixed gas atmosphere.