The　electronic　structures　and　mechanic　properties　of　MX　(M=Sc,　Ti,　V;　X=C,　N,　O)　solids　are　investigated　by　using　density　functional　theory(DFT).　The　results　show　that　the　mononitrides　have　the　greatest　bulk　modulus.　Under　high　compression,　the　calculations　indicate　that　all　compounds　will　undergo　a　structural　phase　transition　from　NaCl　to　CsCl　structure,　and　the　transition　volume　decreases　from　MC　--＞　MN　--＞　MO.　The　band　structures　and　density　of　states　of　each　compound　are　also　calculated　by　DFT　method,　and　the　conductivity　of　this　class　of　compounds　is　discussed.