Abstract: This article deals with the physical process when a high intensity broadband KrF Laser beam passes through gaseous Raman medium. We discuss the parameter dependence of the threshold power and conversion effeciency of SRS.Based on the analysis of SRS initiation and calculation of stoke laser modes formation,as well as the spatial propagation and amplification, we focus on influence of focus position on physical process, especially the Stokes output characteristic.By comparison between experimental results and theoretical expectation,we clarify some ambiguous viewpoints widely existing in the literature of SRS.