As the global almond industry expands rapidly, large quantities of by-products are generated during processing (such as green hulls, shells, and skins), which are rich in functional constituents including polyphenols, flavonoids, dietary fibers, and volatile aroma compounds. This review summarizes the compositional characteristics and extraction technologies of these by-products, while elucidating their potential applications in food and biomaterials, with a specific focus on their antioxidant properties, bioactivities, and structural features. Furthermore, in light of recent research advances, the review further discusses poor stability, low bioavailability, challenges in processing compatibility and other problems, proposing enhancement strategies such as nano-delivery, structural modification, and combined utilization.