Alum is one of the most important materials in the restoration of calligraphy and paintings. However, easy hydrolysis of alum produces acid at high humidity, which can accelerate the hydrolysis and aging of paper cellulose. The pH value, hydrophobicity, color difference and mechanical properties of Xuan paper and color fixing before and after sizing with alum as well as six precipitants with high cationic charges (after hydrolysis) were studied. The surface condition after sizing, including the chemical bonding of precipitants with gelatin and fibers, were tested by scanning electron microscopy (SEM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometry. Also, the species distribution of precipitants after hydrolysis, mixing with glue and sizing on the surface of Xuan paper were studied using high-field ²⁷Al-nuclear magnetic resonance (²⁷Al-NMR) spectrometry. The results show that the pH value of Xuan paper sized by white polyaluminium chloride(PAC) could reach over 7 and the sizing material improved the hydrophobic property and mechanical strength of the paper and made pigments that have good color and no shading. SEM analysis shows that white PAC could cover and fill fibers and pores of Xuan paper uniformly. ²⁷Al-NMR, ATR-FTIR and a curing test show that the content of [AlO₄Al₁₂(OH)₂₄(H₂O)₁₂]⁷⁺(Al₁₃) in PAC was relatively higher, and it also had the effect of promoting the drying of gelatin. It could be bonded with gelatin to form a network complex, which was suitable to replace alum as a sizing precipitant.