This study evaluated the properties of lentil protein, pea protein, quinoa protein, and soy protein as natural nanoparticle stabilizers and their interactions with pectin and chitin nanofiber in preparing high internal phase Pickering emulsions (HIPPEs). The globular plant proteins interact with polysaccharides through hydrogen bonding and electrostatic interactions, transforming the structure into complex morphologies, including fibrous and elliptical shapes. These complex nanoparticles exhibited enhanced thermal decomposition stability, and the HIPPEs constructed by them demonstrated significantly improved apparent viscosity and elastic modulus, with a yield stress of 931.9 Pa, showing gel-like viscoelastic characteristics. The complex system not only reduced droplet size but also formed a compact network structure, which enabled the emulsion to maintain excellent stability under heat treatment, long-term storage and high-speed centrifugation. Our findings revealed the promising potential of utilizing plant-based proteins with polysaccharides to prepare HIPPEs for developing fat alternatives.