Abstract: The chemical compounds co-existed with methyl tert.-butyl ether (abbreviated as MtBE) which was synthesized by the reaction between methanol and mixture of butenes,were separated on DB-624 capillary chromatographic column,identified and determined by GC-MS.The peak area-normalization method was adopted in the determination.Totally,66 compounds (including MtBE itself) were found and their contents (in relative %) given.Formation mechanism of part of the co-existing components,present as impurities,was also discussed.