The method based on ultra-violet fluorescence spectroscopy (IGOSS-IntegratedGlobal Ocean Station System) with aromatic-free petroleum ether as the extractantand chrysene as the intercomparison chemical, for the measurement of petroleumhydrocarbons in seawater is presented in this paper. 1. The comparison between the spectra of the excitation and fluorescence of thechrysene and sample oil extracted from the Dong Hai proved that both of the chryseneand sample oil were excited most strongly in the neighborhood of 310 nm and fluore-sced most intensively at 360nm. Daqing crude oil and its kerosene were scanned withexcitation at 310nm and fluorescence spectrum also showed in the neighborhood of 360nm. There were striking resemblances between the fluorescence spectra of the Deqingcrude oil anple mixed with chrysene and that of chrysene, and it was found thatfluorescence spectrum of mixed oil was simply the sum of the two individual curves 2. Using concentrations of about 0.5μg/ml, the fluorescence intensity of thestandard oil and chrysene was measured. The value of intercomparison ratio "R" wascalculated: Daqing crude oil was 8.7, sample oil extracted from seawater of the DongHai 21. 1. The causes leading in the difference of "R" were discussed briefly. 3. Conditions for sample extracting and the effect of grease or oil from animaland plant on petroleum hydrocarbons have been studied. The linear range of the experiments indicated 0-900μg/1 for chrysence, 0-5000μg/l for Daqing crude oil. Minimum detectable concentration was approximately 2μg/1Daqing crude oil, the standard deviation was ±0.0004mg/l, the coefficient of varia-tion was 3.7% and the average recovery of Daqing crude oil was found to be 91.1%.