Ce-doped α-Fe2O3 nanoparticles were successfully synthesized by hydrothermal method at different pH. The relationship between the pH of the solution and the morphology, structure and electrochemical stability of the prepared Ce-doped α-Fe2O3 nanoparticles was investigated by X-ray diffraction, transmission electron microscopy, scanning electron microscope, Fourier transform infrared, X-ray photoelectron spectroscopy, electrochemical methods and saltwater immersion experiment. The results showed that the Ce-doped α-Fe2O3 nanoparticles prepared at pH = 4 and pH = 6 had surface defects structure, and the Ce-doped α-Fe2O3 nanoparticles prepared at pH = 8 had adhesion structures, which were CeO2 nanoparticles adhered to the α-Fe2O3 nanoparticles’ surface. The fact that Ce ions could be readily doped into the α-Fe2O3 lattice, causing lattice distortion and increasing the binding energy of Fe3+ in the lattice, thereby enhancing the stability of Fe–O bonds correspondingly. At the same time, the surface defect structure is produced, which has the effect of promoting the compactness of the coating. The surface defects structure of α-Fe2O3 has stronger electrochemical stability than the adhesion structure of α-Fe2O3 and Bayer α-Fe2O3. It was found that waterborne acrylic coatings prepared from of α-Fe2O3 with surface defects structure had a stronger hindering effect on the diffusion of charged ions.