A fluorescent optical fiber measuring system used to measure the concentration of the mineral oil in water is put forward in this paper according to the mechanism that the mineral oil in watercan emit fluorescence when excited by ultraviolet light. The pulse xenon lamp is used as excitation light source, while the linear CCD is adopted as the fluorescent signal of photoelectric detection components instead of the traditional photomultiplier tube in the system, combining with the optical fiber sensor technology and weak signal detection technology. It also equipped with the data acquisition card to realize data receiving and A/D conversion, using micro computer to store and display the data. This in turn realizes the accurate measurement of the concentration of mineral oil in water. The fluorescence optical fiber measuring system that used to measure the concentration of the mineral oil in water has the characteristics of simply structure, high sensitivity, wide linear range, probe passive and so on. The experimental result shows that this method is completely feasible.