Abstract: As typical precursors of dioxin, chlorophenols (CPs) are considered as excellent indicators for the concentration of dioxin. A homemade single photon ionization time-of-flight mass spectrometer (SPI-TOF MS) combined with full-automatic enrichment-inlet system was developed for the online determination of CPs. Three Tenax TA adsorption tubes and four solenoid valves were used to accomplish continuous and automatic sampling-enrichment-thermal desorption-inlet. A vacuum ultraviolet (VUV) lamp with photon energy of 10.6 eV was used as the photon ionization source for soft ionization of sample molecules. The molecular ions of the samples generated by SPI were detected by the reflectron TOF MS, and the achieved resolution of the TOF MS was 3 000 (m/z 78). The performance of the instrument was investigated by detecting three CPs (o-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol). As a result, the enrichment factors of o-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol by using the enrichment inlet system are 60, 249, 503, respectively, and the LODs (limit of detection) are 66 pg/L for o-chlorophenol, 120 pg/L for 2,4-dichlorophenol, 125 pg/L for 2,4,6-trichlorophenol. The instrument shows wide dynamic linear range and excellent stability for continuous operation, the dynamic linear ranges are 166 pg/L—16.6 ng/L, 210 pg/L—21 ng/L, 255 pg/L—25.5 ng/L for three CPs respectively. These results show the potential applications for on-site detection of CPs in incineration plants.