The　electronic　structures　of　MC　compounds　(M　=　3d-transition-metal)　in　NaCl　structure　have　been　studied　by　using　the　density　functional　theory　and　the　calculated　results　indicate　that　the　arrangements　of　the　band　structures　and　total　density　of　states　of　MC　compounds　are　similar.　However,　the　chemical　bondings　of　these　compounds　are　different.　According　to　the　components　of　the　energy　bands　crossed　by　Et,　the　MC　compounds　can　be　approximately　divided　into　three　groups,　ScC,　TiC　and　the　other　MC　compounds,　respectively.　By　using　two-sublattice　model,　the　bonding　energies　of　M-C,　M-M　and　C-C　bonds　for　MC　compounds　in　NaCl　structure　are　determined　quantitatively.　The　results　show　that　M-C　bond　has　the　largest　contribution　for　the　cohesive　energy　of　each　MC　compound　and　the　TiC　and　VC　have　the　strongest　M-C　bond,　and　M-M　bond,　respectively.　For　those　metastable　MC　compounds,　the　interaction　between　carbon　atoms　cannot　be　neglected.　Furthermore,　our　calculated　cohesive　energies　of　MC　compounds　in　NaCl　structure　are　in　agreement　with　the　experiments.　(C)　2002　Published　by　Elsevier　Science　Ltd.