The invention relates to a weatherproof inorganic exterior wall coating based on graphene and mullite and a preparation method thereof, and belongs to the field of graphene-based wall inorganic coatings. The weatherproof inorganic exterior wall coating includes the following components by the mass percentage: 5-15% of mullite, 6-15% of perlite, 1-20% of graphene, 2-10% of vitrified micro-beads, 3-10% of sepiolite, 6-15% of albite, 5-18% of light calcium carbonate, 5-10% of bauxite, 2-8% of nano titanium dioxide, 10-15% of nano-silica sol, 20-30% of an auxiliary agent, and 3-6% of a pure acrylic emulsion. The coating has the advantages of strong bonding strength, simple construction and scouring resistance. At the same time, under high temperature conditions, a coating layer is not blistered and cracked or does not fall off, and plays the effects of water prevention, fire prevention, salt resistance, alkali resistance, heat insulation, heat preservation, corrosion prevention, rust prevention and aging resistance.