The invention discloses a 800MPa-level aluminum alloy extruded section and a preparation method thereof, belongs to the technical field of metal materials, and provides a large-size 800MPa-level aluminum alloy extruded section which can be used for semicontinuous casting method preparation. The 800MPa-level aluminum alloy extruded section comprises the following components in percentage by weight:9.0-12.5% of Zn, 2.5-3.5% of Mg, 0.8-1.5% of Cu, 0.08-0.15% of Zr, 0.05-0.25% of Sc, less than or equal to 0.10% of Fe, less than or equal to 0.10% of Si, less than or equal to 0.15% of other impurities and the balance of Al, wherein the percentage of each impurity is less than or equal to 0.05%. The 800MPa-level aluminum alloy extruded section is prepared through the steps of batching the raw materials according to the alloy components, melting the raw materials, carrying out furnace refining and standing, and casting an alloy ingot with a required specification by adoption of a semicontinuous casting method; and carrying out tertiary homogenization processing and extrusion process forming in the conditions that the thickness of the extruded section is not smaller than 40mm and the widthis not smaller than 150mm, and carrying out thermal treatment for using. The novel aluminum alloy extruded section is uniform in microscopic structure and stable in performance; in the L direction, the tensile strength can be above 800MPa, the yield strength can be up to 750MPa and the ductility is higher 8%; in the the LT direction, the tensile strength can be up to 750MPa, the yield strength can be up to 700MPa and the ductility is higher than 6%; and the prepared section can be widely applied in the fields of aviation, spaceflight, nuclear industry, transportation, weapons and the like.