The invention belongs to the technical field of pesticides and particularly relates to a dioxazine derivative as well as a preparation method, a weeding composition and application thereof. The chemical structural formula of the dioxazine derivative is of formula I as shown in the specification, in the formula, X represents N and C which is connected with halogen, alkoxy, alkyl, halogenated alkyl,alkenyl or alkynyl; Y represents N and C which is connected with H, halogen, alkoxy, alkyl, halogenated alkyl, alkenyl or alkynyl; R1, R2, R1' and R2' independently represent H, cyan and the like; R3represents halogen, alkoxy and the like; R4 represents H, halogen and the like; R5 is selected from halogen, C1-C6 alkyl, C3-C6 naphthenic base and C1-C6 alkoxy with or without halogen, and substituted or unsubstituted aryl and heteroaryl. The derivative and the weeding composition thereof are very safe to crops, and are high in medicinal efficiency and good in selectivity.