Nanodiamonds, with good bio-compatibility, chemical stability, drug accommodatingability, fluorescence signals and many other superior properties, have attracted growing attention for anti-cancer drug delivery and bio-imaging applications in recent decades. In this work, the intrinsic Raman signal (1 332 cm-1) of nanodiamonds (NDs) with different sizes synthesized by high temperature high pressure (HTHP) and explosion methods were investigated and compared, in order to select suitable NDs as Raman probes for bio-application, indicating that HTHP synthesized NDs with the size of 100 nm were preferable. NDs were surface homogenized to remove the impurity for further bio-application through acid carboxylation, which was verified with Scanning Electron Microscopy (SEM), Frourier Transform Infared Spectroscopy (FTIR), Raman Spectroscopy and size analysis. And the cytotoxicity of NDs to different cell lines was confirmed with Cell Counting Kit-8 (CCK-8) assay, assuring the good bio-compatibility of NDs and their potential application in bio-system. Besides, based on the sharp Raman peak of NDs at 1 332 cm-1 and the representative Raman vibration band of cells in 2 800～3 000 cm-1 range, NDs were used as Raman bio-probes for the fast localization of NDs in HeLa cells, and the non-invasive dual-color two-dimensional (2D) confocal Raman imaging technique with 532 nm laser was successfully realized. Furthermore, the uptake process of NDs into HepG2 cells was visualized with Raman mapping, revealing the time-dependent behavior of this internalization process. Besides, the endocytosis and localization of NDs as Raman probes by different cells, including HeLa, HepG2, C6 and MDCK cells, were further investigated using the advanced three-dimensional (3D) confocal Raman imaging microscopy, which could render detailed information about the interaction of NDs and cells. And it was observed that the endocytosis of NDs was influenced by cell lines, not only for cancer and non-cancer cells, but also for different cancer cell lines, providing further potential applications for bio-imagingand cancer diagnosis. These results were encouraging and sufficient for following bio-medical studies.