Walnut protein (WalPI) and galactooligosaccharides (GOS) were used as materials for the preparation of WalPI-GOS composite nanoparticles by pH-cycling combined with the ultrasound method and mixed with tea oil to prepare Pickering emulsion. The structure and particle size distribution of WalPI-GOS were characterized by FTIR and particle size analysis. The free sulfhydryl content, thermal stability, and surface hydrophobicity (H0) of WalPI-GOS were determined by fluorescence absorption spectroscopy, DSC, and endogenous fluorescence spectroscopy. The particle size, microstructure, and rheological properties of Pickering emulsion were determined. To investigate the changes in the WalPI-GOS particle and Pickering emulsion properties when the mass ratio of WalPI and GOS was varied from 10:0 to 10:5. The result showed that the WalPI-GOS and Pickering emulsion had the best properties when the mass ratio of WalPI and GOS was 10:4. The particle size, Zeta potential, emulsifying activity index (EAI) and emulsion stability index (ESI) of the WalPI-GOS were 82.08 nm, -52.37 mV, 31.12 m2/g, and 4346.35 min, respectively, which showed good emulsification and stability. Part of the hydrophobic groups of WalPI were embedded inside the WalPI-GOS molecule, which reduced the H0 of the WalPI-GOS (840.81 a.u.) and increased the free sulfhydryl content (8.78 μmol/g) and melting temperature (93.74 °C) of the WalPI-GOS. The complexation of WalPI and GOS changed the secondary and tertiary structure of WalPI to form a secondary structure dominated by β-folding. WalPI and GOS form a compact network structure by hydrogen bonding, electrostatic interaction, and hydrophobic interaction. The particle size of the Pickering emulsion was only 5.24 ?m with uniform droplet distribution, which formed an elastic gel network structure. The Pickering emulsion exhibited the highest apparent viscosity of 1.06 Pa·s at a shear rate of 0.1 s-1. The high cross-linking density between WalPI and GOS enhanced the gel network structure of the Pickering emulsion.