The invention provides a fungus strain and a liquid culture method of mycelia of the fungus strain. The strain is a Fibularhizoctonia sp. fungus of basidiomycota (Basidiomycota), agaricomycetes (Agaricomycetes),atheliales (Atheliales) and atheliaceae (Atheliaceae), and the preservation number is CCTCC M 2018446. The mycelia of the strain are rich in contents of polysaccharide and triterpene compounds, and can be used as novel edible mushrooms for development and application. The mycelia obtained by the liquid culture method disclosed by the invention are good in growth vigor and high in yield,and artificial liquid culture of the strain is successfully realized.