The invention relates to graphene, in particular to graphene and a preparation method thereof. The preparation method comprises the following steps: uniformly mixing a solid organic matter composed ofglucose, citric acid and fructose, with a molten salt composed of sodium chloride, potassium chloride and calcium chloride according to a weight part ratio of 1: 5-100 to obtain a mixture; and heating to 1000-1400 DEG C at a heating rate of 1-10 DEG C/min in an inert gas environment with a flow rate of 100-800 mL/min, carrying out heat preservation for 3-10 h, and carrying out high-temperature thermal polymerization reaction to generate the ultrathin graphene. According to the method, solid organic matters are used as raw materials for synthesizing the graphene, the mixed metal chloride at the molten state at high temperature is used as a solvent, stacking of carbon sheet layers is inhibited, and finally volatilization is performed to generate the ultrathin and ultralight graphene material.