Using density functional theory, we study the alloying of the buckled hexagonal germanene superlattice supported on Al (111)-(3 × 3), the sheet composed of triangular, rhombic, and pentagonal motifs on Al (111)-(3 × 3), and the buckled geometry on Al (111)-(7×7)(19°), which are denoted, respectively, by BHS, TRP, and SRT7, to facilitate the discussion in this paper. They could be alloyed in the low doping concentration range. The stable configurations BHS, TRP, and SRT7 of the pure and alloyed germanenes supported on both Al (111) and its Al2Ge surface alloy, except the SRT7 pure germanene on Al2Ge, could re-produce the experimental scanning tunneling microscopy images. The relatively stable Al–Ge alloy species are the Al3Ge5 BHS-2T, Al3Ge5 TRP-2T, and Al3Ge3 SRT7-1T on Al (111) while they are the Al4Ge4 BHS-1T, Al3Ge5 TRP-2T, and Al27Ge27 SRT7-(3 × 3)-9T on Al2Ge (the n in the nT means that there are n Ge atoms per unit which sit at the top sites and protrude upward). In addition, the Al3Ge5 BHS-2T and Al4Ge4 BHS-1T are the most stable alloy sheets on Al (111) and Al2Ge, respectively. Comparing with the experimental studies, there exists no structural transition among these alloyed configurations, which suggests that the experimental conditions play a crucial role in selectively growing the pure or the alloyed germanene sheets, which may also help grow the one-atomic thick honeycomb structure on idea Al (111).