The changes of microorganism, physichemical parameters and active ingredients during the fermentation of oat with sweet wine starter were studied. The technical parameters were provided to control the fermentation process and judge the end of fermentation. The results showed that pH value decreased rapidly and reached the lowest value of 4.73, and total acid showed a gradual increase to the highest value of 4.84 g/kg during the fermentation of oat. At 48 h, the maximum value ofRhizopus oryzaenumbers, reducing sugar, amino nitrogen and amylase activity were 1.35×104CFU/g, 220.3 g/kg, 352.0 mg/kg and 78.83 U/100mg, respectively. Meanwhile, the sensory score reached the highest value of 96.5. The content of flavonoids β-glucan and total saponins did not change significantly, but the content of flavonoids decreased from 251.2 mg/kg to 179.0 mg/kg during the whole fermentation process. The content of polyphenols increased from 233.6 mg/kg to 505.2 mg/kg and stabilized after 36 h. During fermentation, oat proteins with high molecular weight were significantly hydrolyzed to generate low molecular weight proteins.