Donzens of millimeter-sized freestanding AlN single crystals were grown on the surface of a pre-sintered AlN powder source by the physical vapor transfer (PVT) method. In this paper, the natural growth habits, polarity, and impurity content of the obtained AlN single crystals by this novel approach were analyzed. The results show that the AlN single crystals grown on the surface of pre-sintered AlN powder source have a regular hexagonal shape. The preferential growth direction is along ［0001］ or C-direction with growth rate of 200-250 μm/h, while the radial growth is limited by {10-10} (m-plane). AlN crystals with different colors were sliced into C-axis wafers and then lapped/polished by chemical and mechanical polishing process. The obtained wafers were characterized by selective-wet-etching, and the SEM results reveal that light yellow crystals are Al-polar growth and the dark brown crystals are N-polar growth, while light yellow-dark brown crystals are Al/N mixed polar growth and clear boundaries can be observed between two polarities. Glow discharge mass spectrometry (GDMS) and evolved gas analysis(EGA) were employed to analyze the main impurities in the crystals with different colors. The results show that the content of oxygen in the light yellow crystals is lower than that of the dark brown crystals, while the carbon content is opposite in these crystals with different colors.