Ferric ion with an abnormal concentration level can cause obvious body dysfunction，and even lead to Parkinson's disease，Alzheimer's disease and other serious diseases．Therefore，it is very important to develop an effective analytical method for the detection of Fe,3+, in environmental samples and the dynamic monitoring of Fe,3+, in cells for the maintenance of normal physiological function of human body．In this study，a series of beer-based fluorescent carbon dots（CDs） were synthesized by hydrothermal method using beers as carbon sources．The CDs synthesized with the self-brewed beer of Qilu university of technology had better luminous efficiency than those synthesized with other brands．The structure and optical properties of CDs were characterized by transmission electron microscopy（TEM），X-ray diffraction（XRD），Fourier transform infrared spectroscopy（FTIR），UV-Vis absorption spectroscopy（UV－Vis） and fluorescence spectroscopy．The results showed that the CDs were spherical monodispersed nanoparticles with a relatively narrow size distribution and an average diameter of 5.6 nm，which had an amorphous carbon structure and contained a large number of active functional groups such as C—N/C—O and C,$\stackrel{}{̿}$,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=37289584&type=,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=37289579&type=,3.72533321,2.28600001,O on the surface. The CDs were determined to be composed of carbon，nitrogen and oxygen by X-ray photoelectricity spectroscopy．The CDs shows the property that the emission wavelength changes with the excitation wavelength，and the maximum emission wavelength is 475 nm，showing blue fluorescence．At the excitation wavelength of 400 nm，it has stable fluorescence in the pH range of 3.0－12.0．The effects of UV irradiation time and salt concentration on fluorescence intensity were investigated．The fluorescence intensity decreased by less than 6% even after 6 h UV irradiation．When the salt concentration was up to 0.5 mol/L，the fluorescence intensity did not change significantly．Therefore，the CDs has good optical stability．Based on the specific fluorescence quenching of CDs by Fe,3+,，a sensitive Fe,3+, detection method was established．The linear range was 0.3－45 μmol/L，the correlation coefficient was 0.998 6，and the detection limit was 91 nmol/L．Common metal ions did not cause significant interference．The method has been successfully applied to the concentration analysis of Fe,3+, in tap water，rain water and spring water．The spiked recoveries range from 94.6% to 106%，and the relative standard deviation is less than 5%．Hela cells were used as a model to study the cytotoxicity of CDs by MTT assay．The results showed that the synthesized CDs had good biocompatibility and cell membrane penetration，and were further used for visualization analysis of intracellular Fe,3+, and multicolor cell imaging．This study provides a new idea for promoting the green synthesis of CDs and the development of new analytical methods.