The　clean　and　hydrogen-adsorbed　NbC(1　1　1)　surfaces　are　investigated　using　the　first-principles　method.　For　the　clean　surface,　the　structural　optimization　shows　that　the　spacing　between　the　first　and　second　layer　is　contracted　obviously,　and　the　electronic　structure　of　relaxed　surface　are　compared　with　the　ideal　surface.　Five　hydrogen-adsorption　models　are　studied　and　the　results　indicate　that　the　hydrogen　atom　prefers　to　be　adsorbed　on　the　threefold　hollow　site　in　which　the　third　layer　Nb　atom　sits　directly　below　it.　The　H　1s-induced　state　is　determined　in　the　calculated　band　structure　and　the　reason　why　this　state　cannot　be　observed　in　the　ARPES　is　also　presented　in　this　work.　(C)　2001　Elsevier　Science　B.V.　All　rights　reserved.