The invention relates to the field of preparation of graphene oxide, in particular to a method for preparing graphene oxide. The method comprises the following steps of adding graphite, acid and an oxidant into a material mixing kettle, mixing at low temperature, sending into a first pipeline reactor, and performing oxidizing reaction; adding a solvent and a reducing agent, uniformly mixing, sending into a second pipeline reactor, dispersing and reducing, and performing post-treatment, so as to obtain the graphene oxide. The method has the advantages that the material mixing and reaction types are controlled by pipelines, so that the defect of one-pot boiling type of the traditional kettle type reactor is overcome; the production process is safe and efficient, the product quality is more stable, the continuity of the material in the reaction process is guaranteed, the materials are uniformly mixed, and the utilization rate of the oxidant of potassium permanganate is higher; the oxidizing degree of a product is higher, and the method is suitable for industrialized production.