Abstract: A fiber-optic fluorescence spectrum system is described for detecting carbaryl pesticide residues, which is based on the characteristic that carbaryl can emit fluorescence as it is excited by ultraviolet radiation. The system adopts a kind of configuration of a single light-source, dual light-paths with the functions of detection and reference which have an interference-free capability, uses a cylindrical optical fiber detector designed by ourselves to excite and detect fluorescence, designs the corresponding signal processing circuits, and realizes the microcomputer management.The system can not only detect carbaryl residues, but can detect other residues as well by modifying its some parameters. The experimental results indicate a good linear relationship with analyte concentration in the range of 0～120 μg/L for carbaryl and the detecting limit is 2.7 μg/L as excitation wavelength is 280 nm and emission wavelength is 340nm. It is proved that the system reaches the index of fluorescence detecting.