Abstract: In this study, ultraviolet absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, Raman spectroscopy, scanning electron microscopy and differential scanning calorimetry were used to study the interaction of composite protectants with IgG mechanisms and changes in IgG structure. The results showed that the compound protective agent had little effect on the peptide skeleton of IgG, but had a great effect on the microenvironment of amino acid residues, which enhanced the polarity of the microenvironment of amino acid residues in IgG. The interaction of compound protective agent and IgG mainly involved hydrogen bond, electrostatic force and hydrophobic force, and caused the secondary structure from to changed from α-helix structure to β-folding, β-turning and random curl structure of IgG tended to disorder the secondary structure. The IgG disulfide bond configurations gradually changed from g-g-g to g-g-t and t-g-t. The results of SEM showed that the compound protective agent formed irregular prismatic crystal complexes on the surface of IgG molecules, differential scanning calorimetry showed that the compound protective agent increased the denaturation temperature of IgG from 71.76 ℃ to 87.22 ℃, and decreased the enthalpy change of IgG from 6.51 J/g to 4.68 J/g. The results showed that the conformation of IgG molecule was changed by compound protective agent, which enhanced the thermal stability of IgG.