Diberyllium complexes with an ultrashort metal–metal distance (USMMD, d_M–M < 1.900 Å) are fascinating for the nature of the valence electronic structure of beryllium. In this paper a family of diberyllium complexes, in which Be₂H₃⁺ was coordinated by N-heterocyclic carbenes or mesoionic carbenes, were studied using density functional theory which generated an ultrashort Be–Be distance of 1.754–1.779 Å. Based on bonding nature and electronic structure studies, the ultrashort Be–Be distance was attributed to multiple bonding orbitals and directly orbital overlapping between the two beryllium atoms. These diberyllium complexes exhibited great stability with large HOMO-LUMO gaps and high dissociation energies, and were potential targets in future experiments.