A highly water-soluble fluorescent carbon dots(CDs) was prepared by hydrothermal method using glucose as carbon source，and polyethylene glycol-200(PEG-200) as dispersant and surface modifier. A new fluorophotometric method for the determination of nickel ion was developed using CDs as fluorescent probes，based on the significant fluorescence quenching of CDs in the presence of nickel ion in pH 5.72 Britton-Robinson(B-R) buffer.The maximum excitation wavelength of the system was set at 350 nm and the maximum emission wavelength was 435 nm.Under the optimal conditions, the relative fluorescence intensity of CDs was proportional to concentration of nickel ions in the range of 3.0-80 μmol/L，with a linear regression equation of ΔF= 1.009+0.031 0 c(μmol/L) and a correlation coefficient(r) of 0.998 3.The detection limit was 0.13 μmol/L.The proposed method was applied in the determination of trace nickel in the environmental water samples，and the results were consistent with those obtained by the atomic absorption spectrometry.The spiked recoveries of standard addition were in the range of 98.1%-103.5%, with relative standard deviations(RSD) less than 2%.