Provided are a low-viscosity graphene oxide slurry and a preparation method thereof, a graphene oxide film and a preparation method thereof, and a graphene heat-conducting film and a preparation method thereof. A main method used comprises ultramicro-refining graphene oxide under high-pressure shearing, high-speed impacting and a strong cavitation action to reduce a flake diameter of the graphene oxide, thereby reducing a viscosity of the graphene oxide slurry and increasing a solid content of the graphene oxide slurry, so that an efficiency of coating the graphene oxide slurry into the graphene oxide film is improved.