An amorphous oxacillin fluridone and a preparation method, herbicidal composition and use thereof are provided. The X-ray powder diffraction pattern of the amorphous oxacillin fluridone is free of acute diffraction peaks, and preferably is substantially as shown Fig. 2. The amorphous oxacillin fluridone has better physicochemical stability than the crystalline form A of oxacillin fluridone, and no crystalline transformation occurred within two months of storage at a high temperature of 55°C, purity was not substantially reduced, and water solubility doubled. The herbicidal composition of amorphous oxacillin fluridone and a herbicidal composition of the amorphous oxacillin fluridone compounded with other effective ingredients have a better prevention and killing effect both on gramineous weeds and certain broad-leaved weeds found in corn fields, and so have good application prospects.
