Abstract: The constitute and geometric structure of psilocine was explored by gas chromatography/mass spectrometry (GC/MS). Pliocen is a kind of psychedelic, existing in hallucinogenic mushroom plants. The plants sample was smashed directly with ultrasonic extraction by methyl alcohol, the impurity decontamination was removed by acetone, then introduced directly and treated with microwave derivation for determination. The result showed fragment ion of psilocine was m/z 58(base peak ion), m/z 204(molecular ion). Fragment ion of acetic acid anhydride derivatives was m/z 58(base peak ion), m/z 246 (molecular ion). Fragment ion of BSTFA derivatives was m/z 58 (base peak ion), m/z 73, m/z 290 and m/z 348(molecular ion).