The invention discloses a composite herbicide, which comprises the following components in percentage by 
mass: 5 to 60 percent of oxadiazon, 3 to 50 percent of oxyfluorfen, 5 to 70 percent of 
butachlor, 1 to 20 percent of auxiliaries, and 5 to 80 percent of 
solvent or carrier. A preparation method of the composite herbicide comprises the following steps: putting the oxadiazon and the oxyfluorfen technical into a preparation kettle; adding the 
solvent to dissolve the oxadiazon and the oxyfluorfen technical while stirring; sequentially adding the 
butachlor, the auxiliaries and the 
solvent; and uniformly stirring to obtain an emulsifiable solution product. The composite herbicide has the advantages that: the oxadiazon, the oxyfluorfen and the 
butachlor belong to different types of herbicideswith different functions and characteristics, prevent weeds from generating 
drug resistance after compounded, have complementary advantages to enlarge the range of 
weed control, in particular to noxious weeds difficult to control insects, and can postpone and control the 
drug resistance of weeds and succession of 
weed community in the field; and the herbicide composition has good safety to plantsand afterreap crops.