A gradient electrically conductive-uniform thermally conductive dual network structure-based electromagnetic shielding polymer composite with low reflection and high absorption and a preparation method thereof. The electromagnetic shielding polymer composite includes a gradient conductive carbon nanotube network with a vertically oriented cell structure and a uniformly thermally conductive hexagonal boron nitride/carbon nanotube network constructed by the hexagonal boron nitride dispersed uniformly in the carbon nanotube network and the gradient carbon nanotube network. The gradient electrically conductive carbon nanotube network and the uniformly thermally conductive hexagonal boron nitride/carbon nanotube network form a composite synergistic dual function network structure so as to make the electromagnetic shielding polymer composite have a low reflection and high absorption and excellent thermal conductivity.