The stabilities and electronic structures of Al6CMn (M = Li, Na, K; n = 2, 4, 6) are studied by evolutionary algorithm combined with ab initio methods. The strong attraction of the C4+ core to the valence electrons makes the 2S state considerably lower and the degenerated 2P6 being located in-between the split 1D10 states, so the 26 valence electrons form closed 1S21P62S21D102P6 shells. C-doping enhances considerably the stabilities of metal clusters. In Al6CMn clusters, the Al6Cq− with nearly all the valence electrons form Zintl anions and the M+ cations are ionically bonded on the peripheries. As Li+ has smallest radius, Al6CLi4 possesses strongest thermal and chemical stabilities. The electronic structure of Al6C4− accords with the 8 + 18-electron rule and the Wade-Mingos rule, and can be regarded as a superatomic anion with specific stability. It can be used as building blocks to form Zintl phase structures by combining with metal counterparts.