AlN films grown by high temperature hydride vapor phase epitaxy (HVPE) on Si-face and C-face 6H-SiC substrates were investigated. The influences of the substrate polarity with varied V/III ratio on growth mode, structural characteristics and crystalline quality of hetero-epitaxial AlN films have been studied. With the increasing of V/III ratio, AlN grown on Si-face 6H-SiC substrates changed the growth mode from step-flow to 3D island growth, and correspondingly, its surface morphology got rougher. On the contrast, AlN on C-face substrates were consistently in 3D growth mode and maintained a relatively rough surface, with a high density of nanotubes generated, each of which consisting of hexagonal sides defined by {01 (1) over bar0} facets and locating at the bottom of a V-shaped pit on the surface. Based on XRD, Raman and TEM analyses, it was found that the best AlN layer quality was obtained on the Si-face 6H-SiC at V/III ratio of 10.