In four ratio experiments, natural waters, sampled from the mountain reservoir and the sea water around Dalian city, were mixed with the sewage from petroleum refinery and petroleum exploitation plants. The fluorescence spectra of water samples containing only chromophoric dissolved organic matters(CDOM), samples containing only petroleum, and samples containing a mixture of petroleum and CDOM were analyzed, respectively. The purpose of this analysis is to provide a basis for determining the contribution of petroleum substances and CDOM to the total absorption coefficient of the petroleum-contaminated water by using fluorescence technique. The results showed that firstly, CDOM in seawater had three main fluorescence peaks at Ex: 225～230 nm/Em: 320～330 nm, Ex: 280 nm/Em: 340 nm and Ex: 225～240 nm/Em: 430～470 nm, respectively, and these may arise from the oceanic chlorophyll. CDOM in natural reservoir water had two main fluorescence peaks at EX: 240～260 nm/Em: 420～450 nm and Ex: 310～350 nm/Em: 420～440 nm, respectively, and these may arise from the terrestrial sources; secondly, the water samples containing only petroleum extracted with n-hexane had one to three fluorescence spectral peaks at Ex: 220～240 nm/Em: 320～340 nm, Ex: 270～290 nm/Em: 310～340 nm and Ex: 220～235 nm/Em: 280～310 nm, respectively, caused by their hydrocarbon component; finally, the water samples containing both petroleum and CDOM showed a very strong fluorescence peak at Ex: 230～250 nm/Em: 320～370 nm, caused by the combined effect of CDOM and petroleum hydrocarbons.