This study aimed to improve the preservation effect and extend the shelf life of Lanzhou lily during storage. Potato and pea starches were used as raw materials to optimize oxidized starch preparation via single-factor and response surface experiments. The physicochemical properties of the oxidized starches and their application in the preservation of Lanzhou lily were analyzed. Under optimal preparation conditions, the carboxyl contents of the oxidized potato and pea starches were 0.65% and 0.45%, respectively. The erosion and rupture of oxidized starch grains, along with the appearance of absorption peaks corresponding to carbon-oxygen double bond vibrations, indicated successful oxidation. Crystallinity, swelling capacity, and retrogradation decreased following oxidation, whereas transparency and solubility significantly increased. Oxidized potato starch exhibited a more porous structure, lower heat requirement for swelling, higher storage stability, fewer impurities, and better solubility than oxidized pea starch. The results of the preservation experiment demonstrated that both types of oxidized starch film significantly mitigated quality deterioration during the postharvest storage of Lanzhou lily; notably, however, the oxidized potato starch film provided a better preservation effect than the oxidized pea starch film. The results of this study provide a theoretical basis for the preparation of oxidized starch using hydrogen peroxide and its application in freshness preservation films for fruits and vegetables, and will aid in advancing the field of fruit and vegetable preservation.