Simultaneous determination of four flavonoids in extracts of the fruits of Rosa davurica pall.(FRDP) by high performance liquid chromatography (HPLC) was carried out, and the in vitro activities of extracts of FRDP, four flavonoids and their compound compatibility were measured by UV method. The results showed that the contents of hyperoside, rutin, quercetin and luteolin of the extract of FRDP were 607.98, 450.63, 187.32 and 12.68 μg/g respectively. The extracts of FRDP, four flavonoids and their compound compatibility all have certain antioxidant activities in vitro, and the activity of extracts of FRDP was stronger than that of compound compatibility. However, both of them were weaker than that of VC. The extracts of FRDP, four flavonoids and their compound compatibility also had the activity of scavenging nitrite, blocking the synthesis of nitrosamine and inhibiting α-glucosidase, and the activity of extract of FRDP was stronger than those of acarbose and compound compatibility。