The invention discloses a flexible film electrode and a preparation method thereof, and belongs to the technical field of flexible electrodes. The method comprises the steps of: performing sputter deposition of a Cu thin film electrode on a pretreated SiO2+Si substrate; and performing transfer printing of the Cu thin film electrode to the flexible substrate to obtain a flexible film electrode. Theflexible film electrode and the preparation method thereof can effectively and simply prepare the Cu thin film electrode on the PET or PI flexible substrate. The stress-induced micro-peeling is employed to regulate the sputtering substrate temperature and the film thickness to weaken the binding force of the Cu thin film electrode on the SiO2+Si substrate and regulate and control the micro-nano structure of the surface of the Cu thin film electrode so as to optimize the resistivity of the Cu thin film electrode. The electrode resistivity of the prepared PET or PI flexible substrate is reducedto 3.2*10<-8>[Omega]m.