Abstract: The successful application of the GC/NICIMS technique for the analysis of abuse drugs and pesticides are presented, including organophosphorus, carbamate, pyrethroid, phenothiazine, barbiturates, benzodiaepines, alkaloids and other toxic substances. This study demonstrated that negative CI mass spectrometry may become a valuable tool, specially using negative CI in combination with positive CI and EI in the identification of unknown compound, because it has advantages of simple mass spectrum, obvious structrural information, high sensitivity and very few interference.