The paper mainly investigated the antioxidaative capacity of the soymilk methanol extracts and analyzed the possible existing antioxidants. DPPH (1,1-Diphenyl-2-picrylhydrazyl radical) method and FRAP (Ferric reducing antioxidant power ) method were used to analyze the antioxidative capacity of soymilk methanol extracts. The total contents of phenolics and total flavonoids were identified by colorimetric method.The kinds and contents of bioactivities of flavonoids were identified by ultra-high performance liquid chromatography-quadruple time-of-flight-mass spectrometry( UHPLC- QTOF-MS).The results showed that the methanol extracts of soymilk owned antioxidative activity. The antioxidative values showed no difference between DPPH and FRAP methods. Total phenolics content (285.77±2.93 μg/mL) was higher than total flavonoids content (11.27±0.51 μg/mL) in soymilk methanol extract. The compounds were identified and quantified by UHPLC- QTOF-MS.Among five bioactivities identified, 6,7,4'-Trihydroxyflavone and Rha-Ara-GlcA-SoyB showed positive correlation with their antioxidant values. However, genistein and daidzein perform negative correlation with antioxidant values. 6,7,4'-Trihydroxyflavone may be the main compound attributing to antioxidation of the commercial soymilk .