The invention provides a 3,4(6)-disubstituted-1,3-benzoxazine-2-ketone compound shown in a formula (I). In the formula (I), when a substituent group R1 is -CH3 and a substituent group R2 is H, R3 is H, or 3-CH3, or 4-CH3, or 2-OCH3, or 4-Cl; when the substituent group R1 is H and the substituent group R2 is -CH3, R3 is 3-CH3, or 4-CH3, 2-OCH3, or 3-OCH3, or 4-Cl. The 3,4(6)-disubstituted-1,3-benzoxazine-2-ketone compound has good bactericidal activity on pathogenic bacteria of crops. The formula (I) is described in the specification.