A new method to determine the content of selenium in rohan ginseng using microwave digestion-gas chromatography is established.The detect conditions are as following: in a PTFE digestion jar,0.300 0 g of crushed rohan ginseng is mixed with 6.00 mL nitric acid and 2.00 mL 30% hydrogen peroxide.After microwave digestion, the Se( VI) in digestive juice is reduced to Se( IV) under acidic conditions.Then,1% 4- nitro phthalic diamine( NPDA) solution is applied to react selectively with Se( IV) to form highly stable 5-Nitro-benzo( 1,2,5) selenadiazole.After extraction by toluene,the substance is separated by capillary gas chromatography.In order to retain the qualitative time,electron capture detector was used.The standard curve with relationship between Se content and the peak height is linearly proportional,with equation of y = 744.925x + 0.217 and correlation coefficient of R = 0.998 3.The linear relationship is valid when the selenium content is within the range of 0.005 to 0.025μg/mL.The relative standard deviation( n = 5) is less than 1.1%.The recovery rate is in the range of 98.0% to 100.7%.The lowest detection limit is 0.003 mg/L.This method is accurate,sensitive and practical.