Abstract: This study aims to investigate the effect of the freezing treatment on the structure of pectin in citrus fruits. A series of tests were carried out on the whole fruits of tangerine (Mandarin), orange (Lane Late), and lemon (Eureka Lemon). Three pectin fractions were separated and then extracted with different freezing times and temperatures, namely, water-soluble pectin (WSP), trans-1,2-cyclohexane diamine tetraacetic acid-soluble pectin (CSP), and Na₂CO₃-soluble pectin (NSP). The content and the monosaccharide fractions were also determined after extraction. Meanwhile, Fourier transform infrared spectroscopy (FTIR), molecular weight, nanoparticle size, nuclear magnetic resonance bop (NMR), and scanning electron microscope (SEM) were performed on the WSP, CSP, and NSP of Eureka Lemon. The pre-and post-freezing pectin architectures were obtained after measurements. The results showed that: There was a decrease in the WSP content of the Mandarin, Lane Late, and Eureka Lemon, with the extension of freezing time. Among them, the CSP content increased, while the NSP content decreased slightly. There was a great decrease in the WSP, CSP, and NSP content, with a decrease in the freezing temperature; The monosaccharide fractions showed that the WSP and CSP of Mandarin, Lane Late, and Eureka Lemon were enriched with the galacturonan (GalA), thus accounting for about 60% of the total. The side chains of the neutral sugars consisted mainly of Galactose (Gal), arabinose (Ara), rhamnose (Rha) composition. The GalA proportion decreased by about 10% after freezing 168h, of which a greater impact of the -10 ℃ slow freezing on the GalA chain structure. The NSP was rich in the neutral sugar side chain, where the Ara accounted for about 25%-40% of the more branched chain. There was no outstanding variation after freezing; The side chain analysis showed that the RG structure of the WSP and CSP ranged from 0.002 to 0.05, indicating that the HG region was much larger than the RG one. The NSP ranged from 0.2 to 0.3 in the HG type, indicating that the RG region was much larger than the HG one. In the Rhe RG-Ⅰ type, the linearity of the WSP and CSP was significantly higher than that of NSP. The linearity (RG region) of the WSP, CSP, and NSP were much larger than the HG region after freezing; FTIR analysis showed that the methyl esterification of the WSP, CSP, and NSP in the Eureka Lemon decreased after freezing; Nano-particle size analysis showed that the average nano-particle size of the WSP, CSP and NSP increased after freezing, indicating the worse dispersibility in the solution system easier to be aggregated and precipitated; The SEM showed that there were the great variations in the structure of the WSP, CSP, and NSP after freezing; ¹H NMR showed that there were both α- and β-conformational glycosidic bonds in the three kinds of the pectin in the WSP and NSP after freezing. The molecular weight analysis showed that the molecular weight of the WSP in the Eureka Lemon decreased after freezing. Among them, the molecular structure was destroyed after freezing, and the molecular chain was broken, as the dispersive stability decreased. The findings can provide fundamental insights into the cryostability mechanisms of citrus fruits. The valuable theoretical references can also be offered for quality preservation during frozen storage.