Abstract: OBJECT How to influence constituents of the volatile oil of Herba pog ostemonis owing to different collection time.METHODS used by GC/MS combinati on technology.RESULTS The averagy dry weight of single plant(i.e.output)increase gradually from July to next April,the content of uolatile oil is highest in November.The contents of Pogostemone in the leaf oil are higher in July and September,then decrease gradually with growth time.Pachouli alco hol is higher in September,October and November,lower in other months.The contents of Pogostemone in stem oil are higher in July,October and next Janu ary,lowest in November.The content variation of Pachouli alcohol in stem oil are not obvious in all growth time,higher slightly only after November.Other compounds are not showed their variation law.CONCLUSION the quality of Herba Pogostemonis collected in November is higher if the content of volatile oil is used as a standard of qualify evaluation,the result is in accordance with traditional coll ection experience.