Abstract: To improve the practical utilization of passion fruit peel, this study systematically examined the bioavailability of its active constituents, their dynamic concentration changes during in vitro simulated digestion, and the antioxidant capacities of digestive fluids across different digestive phases. The core objective was to clarify the digestion and absorption patterns of these components and their ability to retain antioxidant properties. Ultraviolet-visible spectrophotometry was used to develop content determination methods for proanthocyanidins, total saponins, crude polysaccharides, and total flavonoids. Via an in vitro gastrointestinal digestion model, the optimal release time, bioavailability, and content fluctuations of active components were investigated, along with the antioxidant activity of each digestive fluid. The developed method demonstrated high precision and yielded accurate, reliable results. The optimal digestion durations for simulated gastric and intestinal juices were 120 min and 60 min, respectively, with the bioavailability of proanthocyanidins, total saponins, crude polysaccharides, and total flavonoids reaching 1.95%, 26.41%, 47.39%, and 16.85%, respectively. Variations in the trends of active ingredients were observed during simulated digestion, and all digestive fluids exhibited significant scavenging abilities against DPPH·, ·OH, and ABTS⁺·. These results confirm that active components of passion fruit peel can be effectively released during gastrointestinal digestion, and their digestive products have potential antioxidant activity correlated with the concentration of the purified extract powder.