Abstract: The solid- substate fermentation of Cordyceps militaris using tartary buckwheat substrate was performed. The difference between the contents of nutritional and functional components and antioxidant activity of before and after fermentation were analyzed. The results showed that the contents of total nitrogen, reducing sugar, soluble sugar and total sugar were much more lower than non-fermentation (total nitrogen, total sugar p<0.01, reducing sugar, soluble sugar p<0.05) , and free amino acids were higher than non-fermentation significantly (p <0.01) . Similarly, functional components like crude polysaccharide, flavonoids, total phenol, anthocyanins, vitamin C, GSH (glutathione) , SOD (superoxide dismutase) of fermented substrate had significant changes compared with non-fermentation (crude polysaccharide p<0.05, others p<0.01) , higher than that.ABTS 2, 2 '- Azinobis- ( 3- ethylbenzthiazoline- 6- sulphonate) of different extracts of tartary buckwheat fermented substrate including petroleum ether, chloroform, ethyl acetate and water part had Antioxidant activities, respectively. The scavenging abilities of ethyl acetate and water part are 100%, equal to TBHQ (Tertiary butylhydroquinone) , BHT (butylated hydroxytoluene) and VC (vitamin C) when concentration was10mg/mL. Analysis of HPLC-MS/MS indicated that ethyl acetate and water part which had the highest antioxidative activity contain rutin, quercetin, substance with quercetin structure fragment, substance with catechin structure fragment and quercetin, rutin, kaempferol-3-rutinose, substance with quercetin structure fragment, substance with kaempferol structure fragment, respectively.