Hydrogen sulfide (H2S) is an important endogenous gas signal molecule in living system, which participates in a variety of physiological processes. Very recent evidence has accumulated to show that endogenous H2S is closely associated with various cancers and can be regarded as a biomarker of cancer. Herein, we have constructed a new near-infrared fluorescent probe (DCP-H2S) based on isophorone-xanthene dye for sensing hydrogen sulfide (H2S). The probe shows remarkable NIR turn-on signal at 770 nm with a large Stokes shift of 200 nm, together with high sensitivity (15-fold) and rapid detection ability for H2S (4 min). The probe also possesses excellent selectivity for H2S over various other analytes including biothiols containing sulfhydryl (-SH). Moreover, DCP-H2S has been successfully applied to visualize endogenous and exogenous H2S in living cells (293T, Caco-2 and CT-26 cells). In particular, the excellent ability of DCP-H2S to distinguish normal mice and tumor mice is shown, and it is expected to be a powerful tool for detection of H2S in cancer diagnosis.