The invention discloses a hot top casting process for a phi 784-mm 7xxx-series superhard aluminum alloy round bar. The aluminum alloy round bar is composed of, by mass, 0.25% of Si, 0.4% of Fe, 1.55-1.65% of Cu, 0.25% of Mn, 2.55-2.65% of Mg, 0.19-0.25% of Cr, 5.6-5.7% of Zn, 0.15% of Ti, 0.03% of Zr and the balance Al. The manufacturing process comprises the steps of a, material preparation; b, smelting; c, stirring; d, refining; e, slagging-off; f, heat preservation and standing; g, online thinning; h, online degassing; i, filtration; j, casting; k, homogenizing. Through the process, the defects, such as cracks, component segregation, bright grains, thick grains and loose pores, which often appear when a direct condensation casting technology is adopted for large-diameter superhard aluminum alloy are overcome, and by the adoption of hot top casting, the defects of surface segregation tumors, thick coarse-grain layers and the like are overcome.