Abstract: The content of 1,3,5-trichlorobenzene in drinking source water was determined by GC-MS with head-space solid phase micro-extraction (HS-SPME-GC/MS). Using 1,2-dichlorbenzene-d4 as internal standard, the 1,3,5-trichlorobenzene in water sample was extracted by SPME with the PDMS extractor for 20 min. The extractor was desorbed for 5 min at the inlet of the gas chromatograph, and separation of 1,3,5-trichlorobenzene was carried out on the DB-624 chromatographic column with programmed temperature elevation. Electron bombardment ionization (230 ℃, 70 eV) and selected ion scanning mode were adopted in MS analysis. Linearity was obtained in the range of 0.100-2.50 μg·L-1, with detection limit (3S/N) of 0.019 μg·L-1. The proposed method was applied to the determination of 1,3,5-trichlorobenzene in river water and reservoir water, and values of recovery obtained by standard addition method were in the range of 91.5%-126.0%.