A preparation method of a graphene film prepared with flexible polyimide includes the following steps: S1, laminating a plurality of polyimide films; S2, performing heat treatment while pressing the laminated polyimide films for bonding, wherein the temperature of heat treatment is lower than the temperature at which a thermoplastic polyimide film begins thermal decomposition, so that the laminated polyimide films are bonded together to form a polyimide composite film; and S3, raising the temperature of the polyimide composite film to be higher than the temperature at which the polyimide film begins thermal decomposition for heat treatment and carbonization treatment, thereby obtaining a carbonized multifunctional film, and performing graphitization treatment as required. The graphene film prepared by the present invention has ultra-high thermal conductivity, excellent flexibility and bending resistance, anisotropy and good electrical boundary shielding effect and magnetic boundary shielding effect, and a good application prospect.