AlN powder was prepared by wet chemical method in NH3 atmosphere using aluminum chloride hexahydrate and urea as raw materials and methanol as solvent. The products were characterized by X-ray diffractometer, scanning electron microscope and laser particle size analyzer. The results show that hexagonal AlN powders with high purity are obtained when the calcination temperature is above 900 ℃. The product obtained at 1 000 ℃ presents spherical characteristics, whose average crystallite size and particle size are 17.0 nm and 159.5 nm. The microstructure of AlN powder was further characterized by high-resolution transmission electron microscope. Combined with selective electron diffraction and Raman spectroscopy, it is further confirmed that the amorphous impurities existing on the surface of AlN powders are not residual carbon generated in high temperature reducing atmosphere, but should be attributed to alumina hydroxide generated by hydrolysis on the surface of AlN powders.