Three-dimensional　(3D)　ZnO　nanostructures,　hierarchical　nanorods　with　trunks　and　branches,　were　synthesized　via　a　multi-step　growth　method.　The　ZnO　trunk-branch　nanorods　are　immobilized　on　glass　substrates　and　their　fabrication　technologies　include　the　deposition　of　ZnO　seed　crystals　by　magnetron　sputtering　and　the　hydrothermal　growth　of　ZnO　nanorods　without　any　directing　agents.　The　sputtering　pressure　for　the　deposition　of　ZnO　seed　crystals　was　varied　and　the　corresponding　effect　on　the　morphology　and　microstructure　of　3D　ZnO　nanostructures　was　characterized　by　various　spectroscopic　and　microscopic　techniques.　The　growth　mechanism　of　ZnO　trunk-branch　nanorods　was　discussed　and　their　optical　property　was　also　explored.　The　multi-level　constructions　of　ZnO　nanorods　would　benefit　their　photo-related　functional　applications.