Disclosed are a ganoderma lucidum mycelium and a preparation method thereof. The ganoderma lucidum mycelium specifically comprises a culture medium composed of rice bran, wheat bran, corn flour and brown sugar. A ganoderma lucidum liquid strain is taken as a strain, an inoculation method and inoculation amount of the liquid strain are well grasped, and a high-quality ganoderma lucidum mycelium finished product is cultured by reasonable arrangement of the production environment. By implementation of the method, the problem that ganoderma lucidum fruiting bodies cannot be produced massively to further affect application of ganoderma lucidum medicine sources due to insufficient wild ganoderma lucidum resources and high artificial cultivation difficulty is solved. Meanwhile, the production and preparation technology of the final product, namely the ganoderma lucidum mycelium, has the advantages of short cultivation period, simplicity, low production cost, high production efficiency, high stability and the like. Besides, the final product, namely the ganoderma lucidum mycelium serving as an additive, is widely applied to the fields of pharmacy, biological health care products, special drinks, functional foods and the like, and is quite good in market prospect.