A new ifber optic sensor based on the oxidation of 2,4-dichlorophenol (DCP) catalyzed by iron(II) phthalocyanine (Fe(II)Pc) was developed for the determination of DCP. The optical oxygen sensing iflm containing lfuorescence indicator Ru(bpy)3Cl2 was used to detect the consumption of oxygen in solution. Moreover, a lock-in amplifier was used to determine the lifetime of the sensor head by detecting its phase delay change. The results reveal that the sensor has a linear detection range of 1.0×10-6-9.0×10-5 mol/L and a response time of 5 min. The sensor also has high selectivity, good repeatability and stability. It can be used effectively to determine DCP concentration in real samples.