The water soluble carbon dots were prepared by hydrothermal reaction with arabia sugar and casein phosphopeptides.Transmission electron microscopy(TEM)，ultraviolet absorption spectroscopy(UV)，fluorescence spectroscopy(FL) and infrared spectroscopy(FTIR) and X-ray diffraction(XRD) were used to characterize the particle size，absorption spectra，luminescence properties and surface groups of the carbon dots.The FL intensity changes in the presence of representative metal ions under the same conditions were investigated to evaluate the selectivity of the carbon dots.The results showed that the average particle size of the fluorescent carbon dots is 4.62nm,and its maximum absorption wavelength is 281nm.The fluorescent carbon dots could emit bright fluorescence in the ultraviolet light with maximum emission wavelength of 414nm.The carbon dots have good water solubility，and the fluorescence emission spectrum is red shift with the increase of the excitation wavelength.FTIR spectra analysis revealed the presence of —COOH，—NH2 and —OH groups are on the surface of the carbon dots，and the XRD peak is about 21°.Tremendous FL intensity decrease was observed by addition of Cu2+ and Fe3+.The reason may be that the ions caused the aggregation of the fluorescent carbon dots，leading to the decrease of fluorescence intensity.The carbon dots are expected to be used as a fluorescent probe for analysis and biological imaging.