A carbazole-based Schiff base CB2 was synthesized and applied as a highly selective and sensitive fluorescent probe for $Cu^{2+}$ in $H_2O$-DMSO (8/2, v/v, pH = 7.4) solution. CB2 exhibits an excellent selectivity to $Cu^{2+}$ over other examined metal ions with a prominent fluorescence "turn-on" at 475 nm. CB2 and $Cu^{2+}$ forms a 1:2 binding ratio complex with detection limit of $9.5{mu}M$. In addition, the $Cu^{2+}$ recognition process is hardly interfered by other examined metal ions.