Objective To improve the physicochemical stability of walnut polypeptide liposomes (WP-L), delay walnut polypeptide (WP) release, and conduct bilayer polysaccharide modification on the WP-L using sodium alginate (SA) and chitosan (CS).Methods The effects of modifications by CS and SA in different mass fractions on the physicochemical properties of WP-L are investigated. Then, the structural morphology of the liposomes is characterized by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. Additionally, liposome stability under long-term storage conditions is examined. Finally, polypeptide release rates, release behavior, sustained-release characteristics, alongside bioactivity changes before and after digestion are evaluated via in vitro simulations of gastrointestinal digestion and release experiments.Results When the mass fractions of CS and SA are 0.6% and 0.5%, respectively, the encapsulation efficiency of WP by the prepared SA-CS-WP-L is up to 90.67%, with a ζ-potential of -17.10 mV. According to TEM observation, SA-CS-WP-L exhibits a spherical vesicle structure with a smooth surface and a core-shell structure. Changes in TEM image contrast indicate successful deposition of CS and SA onto the WP-L surface. In FTIR results, SA and CS form stable complexes on the WP-L surface through hydrophobic interactions and intermolecular hydrogen bonding. During the 19-day low-temperature storage experiment, SA-CS-WP-L still exhibits a high polypeptide encapsulation efficiency (70.77%) and stable physicochemical properties. In vitro gastrointestinal digestion simulations and polypeptide release assays demonstrate that SA and CS modifications effectively delay WP release during digestion while maintaining their sustained inhibitory efficacy against angiotensin-converting enzyme (ACE). Furthermore, WP release follows Fick diffusion behavior.Conclusion Bilayer surface modification of WP-L using SA and CS effectively protects WP and achieves sustained-release performance.