The effects and underlying mechanisms of konjac glucomannan (KGM) on the freeze-thaw stability of corn starch gels were investigated by incorporating different mass fractions of KGM (0.5%, 1.0%, and 1.5%) into corn starch. After three freeze-thaw cycles, syneresis, microstructure, water distribution, and crystalline structure were analyzed using scanning electron microscopy (SEM), low-field nuclear magnetic resonance (LF-NMR), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The results showed that KGM significantly enhanced the water-holding capacity of corn starch gels after three freeze–thaw cycles, with syneresis rates reduced by 9.19%, 14.88%, and 15.01% at KGM addition levels of 0.5%, 1.0%, and 1.5%, respectively. Microstructural analysis revealed that KGM reduced pore size and decreased the proportion of free water within the gel matrix. Crystallographic analysis indicated that starch recrystallization was effectively suppressed by 1.5% KGM, as evidenced by a reduction in gel crystallinity from 11.78% to 8.32% and a decrease in the R1048/1022 ratio from 1.124 to 1.032, suggesting disruption of short-range molecular order. These structural changes are attributed to interactions between KGM and starch, including competitive hydration and steric hindrance, which inhibit ice crystal growth and starch retrogradation. These findings provide a theoretical basis for the development of starch-based materials with improved freeze–thaw stability for frozen food applications.