This standard specifies a method for the determination of trichlorobenzene in Coating products by gas chromatograph mass spectrometry. It is suitable for the determination of trichlorobenzene in oil-soluble Coating products with a content of not less than 2 mg/kg, including three isomers: 1,3,5-trichlorobenzene, 1,2,4-trichlorobenzene, and 1,2,3-trichlorobenzene. The method summary includes that the tested sample is diluted with ethyl acetate solvent and then filtrated into GC-MS, and the trichlorobenzene in the sample is detected by gas chromatograph-mass spectrometry with selected ion scanning mode, and finally quantified by external standard method. The reagents and materials include ethyl acetate solvent, pure products of three isomers, standard stock solution and standard working solution. Instruments include GC-MS, Analytical Balance, filtrate membranes, volumetricflask, and Centrifuge.