A simple and sensitive fluorescence quenching method was developed for the examination of cefadroxil and cephradine.The method is based on the reaction of fluorescein with cefadroxil or cephradine,resulting in the formation of complexes with weak fluorescence,i.e.quenching the fluorescence intensity of the system.By the use of absorption spectroscopy,infrared spectroscopy and quantum chemistry calculation the reaction process of the cephalosporins and the bonding of reaction mechanism were basically analyzed.Based on this,the fluorescence spectrometry method for the determination of the contents of cefadroxil and cephradine was developed:The maximum excitation and emission wavelength was at 483 nm,and 517 nm and 519 nm respectively.The linear calibration curves were obtained over the cefadroxil and cephradine concentration ranges of 0.3-13.5 mg·L^-1 and 0.1-1.2 mg·L^-1 respectively The proposed method has been successfully applied to the examination of the subject drugs in its pharmaceutical dosage with good precision and accuracy.The recoveries are 99.63%-99.91% and 99.71%-100.08% respectively.