The invention relates to a composite material, a high frequency circuit substrate prepared from the composite material, and a preparation of the composite material. The composite material comprises 20 to 70 parts of a thermosetting mixture, 10 to 60 parts of glass fibre cloth, 0 to 70 parts of a powder filling material, and 1 to 3 parts of a curing initiator; the thermosetting mixture is composed of a thermosetting resin and an ethylene propylene rubber; the thermosetting resin is a polybutadiene or a copolymer of the polybutadiene with styrene, wherein the molecular weight of the polybutadiene is lower than 11000Da, the polybutadiene is composed of C and H, and contains more than 60% vinyl; the weight average molecular weight of the ethylene propylene rubber is larger than 100kDa, and lower than 150kDa, the number-average molecular weight of the ethylene propylene rubber is larger than 60kDa, and lower than 100kDa, and the ethylene propylene rubber is a solid material at room temperature. The composite material possesses excellent solvent solubility, and is excellent in operability; the high frequency circuit substrate prepared from the composite material possesses excellent high frequency dielectric properties and better thermal-oxidative aging properties.