The invention relates to the technical field of modified starch, and particularly discloses oxidation crosslinking modified starch and a preparation method thereof. The preparing process of the modified starch includes the steps that starch and a catalyst are added in water to be evenly mixed first, so that a mixed solution is obtained; then the temperature of the mixed solution is raised to 30-50 DEG C, the pH of the mixed solution is 8-10, and then an oxidizing agent is added to be reacted for 2-5 hours; afterwards, a reducing agent is added, the oxidizing reaction is ended, the pH is adjusted to be 9-11, then a crosslinking agent is added to be reacted for 2-6 hours, the pH is adjusted to be 5.0-7.0, solid matter is obtained through suction filtration, and accordingly the preparing process is completed. The mobility of the modified starch is improved, the film-forming property of the modified starch is enhanced, and phase-resisting separation and anti-frost properties are improved; when the modified starch is used as a film-forming agent of a glass fiber impregnating compound, degradation is easy, the quantity of residues is small, the weaving performance is good, and the bad quality problems of yellowing, unevenness, napping and the like of cloth covers can be avoided.