Simulation of the spherical aberration and beam shape of scanning X-ray source for X-ray Photoelectron Spectroscopy(XPS) has been investigated for optimization of optics and estimation of beam size. The scanning X-ray source used for this study is equipped with an elliptical mirror to diffract and focus aluminum Kα X-ray. The anode from which X-ray is excited, is located on the elliptical mirror focal point, and X-ray source point is projected near the other side of the focal point(sample). At the optical center, it is simulated that there exists no spherical aberration. On the other hand, lineally increasing spherical aberration is observed according to the distance from the optical center both in a horizontal and vertical direction. It is concluded that 10μm beam is applicable if tolerance of alignment is within ±40μm both in horizontal and vertical direction. Using a tungsten mesh(grid) sample, the X-ray beam shape is experimentally measured as 8.7×10.5gm beam. These values are compared with those obtained by simulation and some of the factors influencing results are discussed in detail.