Abstract: A portion of coking wastewater (500 mL) was extracted thrice with CH₂Cl₂ (200 mL for each extraction) in succession, to have the polycyclic aromatic hydrocarbons (PAHs) transfered into the organic phase. The extracts were combined, dehydrated and evaporated to 0.5 mL, and d-12 perylene solution (50 μL) was added as internal standard and the volume of the solution was made up to 1 mL, which was then introduced into the instrument for GC separation using comprehensive 2-dimensional GC column system (1-dimensional RTX-5MS weakly polar column and 2-dimensional DB17-MS polar column connected in series by capillary tube) and the 16 PAHs were determind by TOF-MS. Due to the application of 2-dimensional GC separation, with optimuzation by modulation and deconvolution of the co-effused peaks, the 16 PAHs, including those compounds having very close boil pounts and similar polarities, were separated completely, with fine selectivities and less background interferences, and values of S/N ratio>100 were obtained even for those trace components (10 pg) giving very weak signals. Values of detection limits (3S/N) for the 16 PAHs were found in the range of 0.01-0.092 μg·L^-1, and RSDs (n=5) found from their determined values ranged from 2.5% to 5.0%. By using the data-processing software of the instrument, method for comparative study of total organic compounds in wastewater of this kind was established and used for comment on changes of composition of organic compounds in such wastewater before and after bio-chemical treatment.