The aging of proteinaceous binders buried under soil environment may cause a change of amino acid content, thus affecting their GC-MS identification. In order to improve the accuracy of this method, the author studied how the amino acids of the commonly used binders (collagen, egg and milk) changed after aging in archaeological soil, using GC-MS box plot and principle component analysis (PCA) graph. The GC-MS results show that the levels of Pro, Asp and Glu increased while that of Ser decreased. Gly and Hyp in pig glue and Ile, Phe in egg and milk decreased. These changes caused variations in the box plot and PCA graph, but they were identifiable. Based on the above research, animal glue, and a mixture of animal glue and egg were identified in the painting layers of murals and pottery of the Tang tomb at Guodu, Xi’an. This study has improved the accuracy of GC-MS identification of proteinaceous binders and could provide a scientific basis for exploring the degradation mechanism and selecting proper conservation materials.