The low control accuracy and large fluctuation of the composition and microstructure in the micro-scale of the material are the fundamental reasons restricting the localization process of high-speed train aluminum alloy. Therefore, studying the composition uniformity of large size aluminum alloy from the micro scale is very important. Because the research area of microsegregation in aluminum alloy is usually small, the research method of macrosegregation is too simple. In this paper, the distribution results of alloy elements in the 7B05 aluminum alloy sheet were obtained by micro-beam X-ray fluorescence, and the composition distribution data were analyzed from the point, line, surface, frequency distribution. The results show a segregation band of about 2 mm in the central layer of the cast and rolled 7B05 aluminum alloy section. Al, Cr, Ti and Zr are positive segregation elements, and the content of the central layer is higher than that of the upper and lower layers. Cu, Fe and Zn are negative segregation elements, and the content of the central layer is lower than that of the upper and lower layers. The results show that the degree of statistical segregation of each element is small as a whole, the most uniform distribution is the Al element, and the minimum degree of statistical segregation is 0.01. The distribution of Ti and Fe elements is not uniform, and the degree of statistical segregation is 0.81 and 0.6 respectively. The obvious point segregation of Fe and Mn in the plane distribution is since the intermetallic compounds formed by microscopic segregation during the casting process break into several continuous arranged second phases during the subsequent hot rolling forming. Laser-induced breakdown spectroscopy (LIBS) is used to verify the data obtained by this method. The results show that the surface distribution and line distribution of elements measured in the size range of 168 mm² are consistent with the fluorescence results, proving this method's repeatability and reliability. In conclusion, the calculation of point, line, plane, frequency distribution and segregation degree of the cast and rolled 7B05 aluminum alloy by using the method of micro-beam X-ray fluorescence combined with in-situ statistics can provide a large amount of analytical data, which is of great significance for the quantitative study of the fluctuation trend of microstructure and properties of rolled sheet in a large size range.