Alzheimer's disease (AD) is an irreversible degenerative disease of the central nervous system. In view of the shortcomings of AD diagnosis methods, such as strong subjectivity, time-consuming, invasive, non-invasive, high accuracy, real-time diagnosis of near-infrared spectroscopy (NIRS) analysis has great advantages. In this paper, the spectral information of 265 serum samples that have been diagnosed as healthy and AD was collected, spectral analysis and principal component analysis (PCA) were carried out, and finally combined with aquaphotomics analysis. The results showed that in the first three PCA scores of patients with AD, PC1 tended to be negative, which was different from that of healthy people. In combination with aquaphotomics analysis, it was found that the absorbance of AD patients at the place where the water spectral pattern (WASP) was multi-hydrogen bond and OH stretching was higher than that of normal people, and the probability of the existence of macromolecular groups of water in serum was higher. On the contrary, the absorbance of normal people in free water with single hydrogen bond, hydration and no hydrogen bond is significantly higher than that of AD patients, and the probability of small molecular groups of water in serum is higher. Therefore, the diagnosis method of AD based on NIRS combined with aquaphotomics is feasible.