Uses the highly effective liquid phase chromatography to determine seven kinds of three pyridine class weed killers in soil: Simazine, Arab League Tela Tianjin, Suppresses passes, Green bristlegrass extinguishes only, Suppresses Tianjin, Throws oneself the grass only, and Goes to grass only. Firstly, use the mixture of second grade nitrile or methyl alcohol : second grade nitrile(3:7 v/v)by Rope extractor to extract them out from soil. Secondly, evaporates the extract after circumgyrating it. Thirdly, use nitrogen to blow and concentrate the extract. Fouthly, use neutral aluminum oxide column to purify the extract. Fifthly, use nitrogen to blow and concentrate the extract again. Then use the highly effective liquid chromatography diode array detector to detect the extract by the external standard method at the wavelength of 224 nm. The result indicated that the variation coefficient of this method ranged from 1.24% to 6.83%, the mean recovery ranged from 95.0% to 106.95%, and the detection limit ranged from 0.84 to 2.07μg/kg. It was a proper method to determine seven kinds of three pyridine class weed killers in soil.