The present invention relates to a method for preparing graphene oxide by cutting an end face of a 3-dimensional carbon-based material by electrochemical oxidation and the graphene oxide prepared by the method. The method comprises connecting a piece of a 3-dimensional carbon-based material as an electrode and another piece of a 3-dimensional carbon-based material or inert material as another electrode to the two electrodes of a DC power supply. A working face of one piece of 3-dimensional carbon-based material contacts the surface of an electrolyte solution, and the two pieces are electrified for electrolysis, during which the working face is between -5 mm below and 5 mm above the surface of the electrolyte solution. The graphite lamella on the end face of one piece of the 3 dimensional carbon-based material used as an electrode is expansion-exfoliated and cut into graphene oxide by electrochemical oxidation, to obtain a graphene oxide-containing electrolyte solution.