Polyhydroxy flavonoids are usually sensitive to heat and readily degraded into other structural forms upon thermal processing, to negatively affect their health effects or even total loss. Previously, a major flavonol, quercetin, was the most studied. However, few studies on thermal degradation of dihydroflavonols in aqueous solution have been carried out so far compared to flavonols. Different from the C2-C3 double bond of flavonols, the single C2-C3 bond of dihydroflavonols may cause them to have different degradation mechanisms than that of flavonols. Dihydromyricetin (DMY) is a health-beneficial dihydroflavonol, with six hydroxyl groups. The thermal degradation process and products of DMY in neutral aqueous solution (pH 7) at 100℃ was explored using ultra-performance liquid chromatography combined with photodiode array and electrospray ionization quadrupole-time-of-flight tandem mass spectrometric detection (UPLC-PDA-ESI-QTOF–MS/MS). Thermal treatment led to a decline in DMY level with time, accompanied by the appearance of various degradation products of DMY. Degradation mechanisms of DMY included isomerization, oxidation, hydroxylation, dimerization and ring cleavage. Moreover, the heating treatment on DMY aqueous solution was found to gradually reduce the antioxidant activities of DMY, and even destroy the beneficial effect of DMY on the gut microbiota composition.