Abstract: Biological tissue was weighed 5g, and was whisked to become the jam-like and was prepared the solution sample with use of the mixture of methanol, water and hydrochlororic acid. Gelsemine was extracted from the solution sample by liquid-liquid extractive method. The effect of the impurity in biological sample for the gas chromatography-mass spectrometry (GC/MS) measuring was minimized by fast rising temperature. The main characteristic peaks m/z108(basic peak), m/z251, m/z279 and m/z322(M +) were detected by the selective ion monitoring (SIM) mode under the optimizing GC/MS parameters. Therefore, the molecular formula(C 20H 22N 2O 2), molecular weight (322Da) and molecular structure were determinated. Therewith, a extraction and analysis method of this poison was found for the judicial identify.