The invention relates to a preparation method of 1,7-dihydroxy-perylene-3,4,9,10-tetracarboxylic acid diimide by direct oxidization of perylene-3,4,9,10-tetracarboxylic acid diimide. The method mainly comprises the following steps: the perylene-3,4,9,10-tetracarboxylic acid diimide compound is reacted in sulfuric acid for 10 hours to 30 hours with the existence of an oxidizing agent and at the temperature of 10 DEG C to 40 DEG C, then a reducing agent is added into the reaction system, the heating and refluxing are carried out for at least one hour, filtration is carried out, and a filter cake is washed to be neutral and dried to obtain the target compound. The preparation method provided by the invention has the advantages of simple steps, mild reaction conditions, high reaction yield (98% at most), and the like.