K-frames　are　the　generalizations　of　frames.　In　this　paper,　we　introduce　the　definition　of　a　tight　K-frame　in　a　Hilbert　space,　then　we　give　a　characterization　for　tight　K-frames　by　the　synthesis　operator　and　the　operator　K.　By　means　of　the　operator　K,　we　also　obtain　a　necessary　and　sufficient　condition　for　tight　K-frames　to　be　tight　frames.　In　the　end　we　make　a　discussion　on　the　construction　for　tight　K-frame　and　the　correlations　between　two　tight　K-frames　and　the　involved　operator　K.