The invention discloses a method for detecting content of nitromethane in a cigarette main-stream smoke gas phase by adopting a cold trap-gas chromatography/mass spectrometry. Isopropanol-dry ice is adopted to cold trap nitromethane in the cigarette main-stream smoke gas phase by virtue of methanol solvent under a low-temperature condition (less than or equal to -70 DEG C), a nitromethane-d3 internal standard is accurately added, after being uniformly shaken by a hand, a sample is detected by utilizing gas chromatograph/mass spectrometry, retention time and an ion abundance ratio are used for determination on nature, and characteristic ions are used for determination on quantity. The gas chromatograph/mass spectrometry is used for accurately and quantitatively analyzing the content of nitromethane in the cigarette main-stream smoke gas phase, and the method is good in repeatability, simple to preprocess, easy to operate, high in recovery rate and capable of realizing accurate determination on content of nitromethane in the cigarette main-stream smoke gas phase.