NOVELTY - A graphene powder is prepared by (A) using electric conduction graphite on positive pole of electrolytic cell and inert cylinder electrode on negative pole; (B) applying 10-25 V of direct voltage between positive pole and negative pole for 1-30 seconds; and (C) filtering and washing with deionized water, drying, dispersing in organic solvent according to ratio of 100 mg:50-500mL, oscillating via ultrasound to obtain turbid liquid, centrifuging turbid liquid for 1-10 minutes at 1000- 3000 revolutions/minute, collecting clear liquid containing graphene, and drying to obtain graphene.    USE - Method for preparing graphene powder (claimed) used in lithium ion battery, super capacitor, solar battery, electro-catalysis and bioanalysis and biosensor.    ADVANTAGE - The method reduces pollution to environment and reduces production cost. It has simple and rapid preparation process and is easy for industrial production, as compared with prior art.    DETAILED DESCRIPTION - Graphene powder is prepared by (A) using electric conduction graphite on positive pole of electrolytic cell and inert cylinder electrode on negative pole; (B) applying 10-25 V of direct voltage between positive pole and negative pole for 1-30 seconds; and (C) filtering and washing with deionized water, drying to moisture content below 500 ppm, dispersing in organic solvent according to ratio of 100 mg:50-500mL, oscillating via ultrasound to obtain turbid liquid, centrifuging turbid liquid for 1-10 minutes at 1000- 3000 revolutions/minute, collecting clear liquid containing graphene, drying to obtain graphene. The step (A) comprises using electric conduction graphite on positive pole of electrolytic cell and inert cylinder electrode on negative pole, where space between positive pole and negative pole is 1-10 cm, and electrolyte is water system electrolyte or non-water system electrolyte; and applying voltage of 0.1- 2.5 V for 1-10 minutes between positive pole and negative pole. Electric conduction graphite is natural graphite, natural modified graphite, synthetic graphite, expanded graphite and high orientation pyrolytic graphite, where particle size is 5-20 mu m, size of schistose is 1-5 cm2, carbon content is more than 99.5%. Water system electrolyte is hydrochloric acid, sulfuric acid, nitric acid or soluble lithium salt (20-50 mg/mL), where pH value is 0.50-10.00. Non-water system electrolyte is electrolyte containing propylene carbonate (more than 30 mass%), imidazole, pyridine or pyrrole ionic liquid. The oscillating process is carried out at 5-30 KHz and 100-1000 W for 3-10 minutes. Organic solvent is N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, isopropanol, N-methylpyrrolidinone, butanone, acetonitrile, dichloromethane, chloroform, diphenyl ether and/or dichloropropane.