Background Protein–polysaccharide complexes have been widely used to stabilize high‐internal‐phase emulsion (HIPEs). However, it is still unknown whether soy protein isolate–dextran (SPI–Dex) complexes can stabilize HIPEs or what is the effect of Dex concentration on the HIPEs. Furthermore, the non‐covalent interaction mechanism between SPI and Dex is also unclear. Therefore, we fabricated SPI–Dex complexes and used them to stabilize HIPEs‐loaded quercetin and explore the interaction mechanism between SPI and Dex, as well as the effect of Dex concentration on the particle size, ζ‐potential, microstructure, rheology, quercetin encapsulation efficiency, and gastrointestinal fate of the HIPEs. Results Spectral analysis (fourier transform infrared spectroscopy, ultraviolet spectroscopy, and fluorescence spectroscopy) results identified the formation of SPI–Dex complexes, and indicated that the addition of Dex changed the spatial structure of SPI, whereas thermodynamic analysis (ΔH > 0, ΔS > 0) showed that hydrophobic interactions were the main driving forces in the formation of SPI–Dex complexes. Compared with HIPEs stabilized by SPI, the SPI–Dex complex‐stabilized HIPEs had smaller particles (3000.33 ± 201.22 nm), as well as higher ζ‐potential (−21.73 ± 1.10 mV), apparent viscosities, modulus, and quercetin encapsulation efficiency (98.19 ± 0.14%). In addition, in vitro digestion revealed that SPI–Dex complex‐stabilized HIPEs significantly reduced the release of free fatty acid and improved quercetin bioaccessibility. Conclusion HIPEs stabilized by SPI–Dex complexes delayed the release of free fat acid and improved the bioaccessibility of quercetin, and may be help in designing delivery systems for bioactive substances with specific properties. © 2022 Society of Chemical Industry.