Alum gelatin solution is the traditional Chinese materials for paper relics, but excessive use of alum will cause XUAN paper to varying degrees of acidification. In order to understand the effects of alum in alum gelatin solution on different ingredients in XUAN paper, the effect of alum on cellulose, calcium carbonate and gelatin in Xuan paper was studied. The effect of alum on celluloseand calcium carbonate in XUAN paper was studied by attenuated total reflectance Fourier transfer infrared (ATR-FTIR) spectroscopy and X-ray diffraction(XRD). For the first time, the effect of alum on gelatin in Xuan paper was studied by Fourier self-deconvolution and curve-fitting techniques. XRD and ATR-FTIR results showed that the alum dissolved cellulose and calcium carbonate in the paper and produced calcium sulfate. When the concentration of alum exceeded 5 Wt%, the composition changed the most violently; Fourier self-deconvolution and curve-fitting results showed that alum would change the secondary structure of gelatin protein on XUAN paper, α-helix, β-turn and γ-random structures were transformed into β-sheet structures. When the concentration of alum exceeded 5 Wt%, the secondary protein structure changed the most violently. In this paper, the effect of alum on different ingredients in Xuan paper was expounded, and the dosage range of alum was given on the basis of minimum interference principle. In addition, a new method has been introduced to study the secondary structure of protein in paper relics, and the application range of ATR-FTIR in paper relics has been expanded.