The chemical composition of flavonoids in sea buckthorn leaves is summarized, and different extraction methods (organic solvent extraction, ultrasonic-assisted extraction, microwave extraction, and supercritical fluid extraction) and purification technologies (decolorization of macro-porous resin and decolorization of magnetic multi-walled carbon nanotubes) of flavonoids in sea buckthorn leaves are also introduced. In addition, the hypolipidemic effect of flavonoids from sea buckthorn leaves is summarized. Finally, the regulatory mechanism of flavonoids in mouse hypolipidemic effects is also explained.