Abstract: Rotating ellipsoidal mirror is an ideal reflective X-ray focusing device. An X-ray optical tracing method based on Matlab to realize the focusing simulation of the ellipsoidal mirror was proposed. The factors affecting the focusing effect of the ellipsoid mirror were summarized, and the X-ray optical tracing model was established. The focusing simulation of two groups of small-diameter ellipsoidal mirrors with a length of 50 mm was carried out at the energy of 8 keV, and the focusing characteristic parameters such as the focal spot size and average reflectivity were analyzed. At the same time, the annular spot under defocus was simulated. The influence of the surface height error and surface roughness on the focusing effect of the ellipsoidal mirror was discussed. The light source intensity distribution information was introduced, and the focusing spots of the average distribution and Gaussian distribution light sources were simulated, respectively, under the condition of surface light source with a diameter of 7 μm. This simulation method supports the independent setting of the ellipsoidal mirror size, surface reflectivity, surface error, light source characteristics and other information. It is both scientific and flexible, and can be used as a convenient tool for intuitively studying the focusing spot and focusing characteristics of the ellipsoidal mirror.