The invention discloses a liquid chromatography-tandem mass spectrometry method for measuring 18 semi-volatile organic pollutants in water. According to the method, a clean water sample such as surface water, drinking water, and the like is simply filtered by a 0.22 [mu]m micro-porous filter membrane, and then a liquid chromatography-mass spectrometry instrument is used to separate and detect the following 18 compounds in water: aniline, benzidine, acrylamide, picric acid, carbaryl, deltamethrin, microcystic toxin-LR, dibutyl phthalate, bis(2-ethylhexyl) phthalate, dichlorvos, trichlorphon, parathion, methyl parathion, malathion, dimethoate, demeton, atrazine, and carbofuran. The provided method can detect many target substances. The detection range of the method is 0.001 to 0.49 [mu]g / L, the relative standard deviation is 0.7 to 15.4%; and the analysis method has the advantages of high sensitivity, quick analysis speed, little pollution, and simple and efficient pretreatment, is especially suitable for standard analysis of drinking water source monitoring, and solves the problems of bad conformability, large labor strength, and low analysis efficiency of the conventional standard method.