The invention discloses a preparation method of large-size 
graphene oxide or 
graphene. The preparation method mainly utilizes 
graphite as a 
raw material and comprises that 1, under the action of an intercalator and an expanding agent, 
graphite fully releases interlayer spaces so that interlayer interaction is reduced and a 
graphene aggregate is obtained, 2, the graphene aggregate is oxidized by an 
oxidizing agent, and then the oxidized graphene aggregate is peeled in water under gentle mechanical action so that a large area of a dispersion liquid of graphene 
oxide is obtained, and 3, the peeled graphene 
oxide is reduced by a 
reducer or heat treatment so that 
high conductivity graphene is obtained. The preparation method utilizes cheap raw materials, has a simple process, can be controlled easily, realizes fast and high efficiency 
solid-liquid separation, is convenient for industrial large scale production, prevents graphene 
crystal structure destroy caused by 
high energy supersonic wave, high speed shearing or fluid crushing. The obtained graphene has a 
large size and 
high conductivity and can be popularized and used in fields of high efficiency 
heat management, 
flexible display, energy conversion and storage.