Abstract: In order to enhance the fatigue resistance of copper-based flexible thin films, copper-coated carbon nanotubes (CNTs) were incorporated into the ink formulation to prepare copper-based composite films, with a focus on analyzing the influence of copper-coated CNTs content on the microstructure and fatigue resistance of the composite films. The impact of copper-coated CNTs content on the microstructure and fatigue resistance of the composite films was emphasized and examined. The results indicated that when the copper-coated CNTs content was 1%, a highly conductive and fatigue-resistant copper-based composite film was obtained, with a resistivity of 17.73 μΩ·cm and the resistance change rate of 49%. This was attributed to the copper-coated CNTs being connected within the interstices of the copper structure, thereby serving as additional conductive pathways that improved conductivity. And it prevents dislocation movement at grain boundaries, delays crack propagation, suppresses the formation of sintering necks, and improves the fatigue resistance of composite films. Due to the minimal interfacial difference between the copper-coated CNTs and the copper matrix, diffusion occurs to the matrix surface during sintering. This results in a reduction of the surface area of the matrix, leading to the precipitation of copper particles. When the content of copper-coated CNTs increases to 2%, the volume and number of copper particles increase, causing a deterioration in the continuity of the microstructure. Consequently, this reduces the electrical conductivity and fatigue resistance of the composite film. Therefore, an appropriate amount of copper-coated CNTs can enhance the electrical conductivity and fatigue resistance of the composite film.