The present invention relates to a hierarchical structure of graphene-carbon nanotubes and a method for preparing the same, and, more specifically, to a method for growing graphene into carbon nanotubes having a hierarchical structure by adding metal nanoparticles on the graphene. According to the present invention, carbon nanotubes having a hierarchical structure, which have an increased specific surface area compared to existing carbon nanotubes, can be obtained, and a carbon nanotube structure which is metal-functionalized by a metal precursor can be obtained. In addition, carbon nanotubes can be prepared in an environmentally-friendly manner by the use of microwaves.