Abstract: To establish a quantitative method for the simultaneous measurement of the residual level of three pesticides in Dendrobium aurantiacum by GC-MS/MS. The samples were extracted by acetonitrile and purify by Cleanert TPH column. The samples were then tested by GC-MS/MS. Information on relative retention time and mass charge ratio was used for qualitative analysis. The peak area obtained by secondary ion MS of dimethoate（125.0/79.0） was used as the reference peak to establish a method using dimethoate as the reference substance to determinate there sidual quantity of three pesticides in Dendrobium aurantiacum by GC-MS/MS. When the injection quantity of the sample containing dimethoatea, dichlorvos and chlorpyrifosis in the range of 0.1~1.0 ng, there is a good linear relationship between the injection quantity and peak area. Limit of quantification（LOQ） of dimethoate, dichlorvos and chlorpyrifos are 1.399×10^-2、2.279×10^-4、1.757×10^-4 ng; The average recovery rates of dimethoate, dichlorvos and chlorpyrifos are 95.4%, 95.0% and 94.7%. the method is simple, accurate, rapid and is appropriate for the quantification of residual quantity of dimethoate,dichlorvos and chlorpyrifos in Dendrobium aurantiacum.

Key words: GC-MS/MS, Dendrobium aurantiacum, dimethoate, dichlorvos, chlorpyrifos