L-ascorbic acid (ASC) is well-known for its excellent antioxidant properties. In addition to its significant role in maintaining human health and preventing scurvy, ASC is widely used as an effective antioxidant in the food industry. Despite its widespread application in liquid foods, ASC is poorly stable in aqueous solutions, where it readily degrades under light and heat. To improve the stability of ASC in aqueous solutions, this study employed co-crystallization technology, using liquid-assisted ball milling to prepare eutectic mixtures of ASC with sucrose (SUC), D-glucose (GLU), and trehalose (TRE). The results demonstrated that all eutectic mixtures exhibited significantly lowered melting points. The microstructure of the eutectic mixtures was transformed from irregular large blocks to uniform small particles. Under pH conditions of 3.50, 4.50, and 7.00, the stability of eutectic ASC mixtures was 1.05, 1.17, and 1.78 times higher, respectively, than that of pure ASC, with the most effective protection under neutral condition. The SUC-ASC-1.5 H eutectic mixture, which had the highest stability across the pH range, was selected for further study. It demonstrated optimal stability in acidic environments, being 1.09~1.33 times higher than that of pure ASC after exposure to high temperatures and UV light. In this study, three types of sugar–ASC eutectic mixtures were successfully prepared and their ability to inhibit the oxidative degradation of ASC in aqueous solutions under unfavorable processing conditions was demonstrated. The findings offer a new method for enhancing ASC stability in aqueous environments and provide new research directions for developing more stable ASC-based functional foods and health products.