Comparing the results of AlC cluster, computed by 7 methods of density functional theory (DFT), with experimental data, we choose B3lyp/6-311G(d) to optimize the structures and analyse the frequencies of AlnC and AlnC+(n=1—8) clusters. All ground states and metastable states of AlnC and AlnC+ clusters are obtained. Our calculations reveal that there exists a transition from planar to spacial structures with the number of Al atoms increasing. Planar structures is mostly triangle and spacial structure is primarily triangular prism cage structure. Of the high symmetry clusters, only one of neutral and cation has a stable structure. Compared with various kinds of AlnC and AlAlnC+(n=1—8) clusters under study, Al2C and Al5C are stable.