The effect of sodium alginate amount on the stability of whey protein solution was studied. The result showed that with the increase of sodium alginate amount, the ζ-potential of the whey protein-based solution decreased gradually, and the particle size and turbidity of the whey protein-based solution increased first and then decreased, and the microstructure of microscopy and fluorescence microscopy changed from disorder to uniform order. When pH value is close to the innate point of the whey protein isolate, the stability of the whey protein-based solution was better than that of whey protein solution. When NaCl concentration increased to 0.20 mol/L, the stability of the whey protein-based solution was weakened obviously. In the microscope image, the complexes flocculate and the fluorescence appears to accumulate. When the mass ratio of whey protein and sodium alginate was 3∶2.5, the stability of the whey protein-based solution was the best. The results showed that sodium alginate improved the stability of the whey protein solution significantly, which can expand the use of whey protein isolate and provide technical reference for the application of whey protein-based solution in food industries.