The invention relates to a method for preparing 2, 4-dinitrobromobenzene by bromobenzene, which comprises the following steps: adding metered bromobenzene and water into a reactor; heating to the temperature of 80 DEG C and beginning to drip mixed acid of nitric acid and sulphuric acid; controlling reaction temperature at 80 to 100 DEG C and reaction time for 1.5 to 2.5 hours; cooling, filtering,washing by water and drying the reactant to obtain a light yellow solid crude product; and recrystallizing the crude product by ethanol and drying the crude product to obtain the pure product, wherein the productive rate of the pure product is 91.0 to 97.0 percent and the purity is more than than 99 percent. The method has the advantages of simple operation, easy separation and purification for the products, high yield, low cost, little environment pollution, and the like.