Abstract: The present invention relates to a method for synthesizing carbon nanowires directly on the internal surface of a three-dimensional structure including a carbon structure and, more particularly, to a method for synthesizing carbon nanowires at high density on the surface of pores or gaps present in a structure, and a hierarchical structure synthesized by the method. According to the present invention, it is possible to fill fine pores or gaps in a structure, which cause a reduction in mechanical properties or conductivity, with high-density carbon nanowires, thus significantly improving mechanical or electrical performance of a final product.