AlN single crystal film was grown on 6HSiC substrate by hydride vapor phase epitaxy (HVPE). The thermodynamic theory was used to calculate the mass balance in the source region of AlNH system. It is indicated that when the source temperature is set to 800～900 K, the partial pressure ratio of HCl and AlCl3 will be 1∶3, and the main reactant will be AlCl3 which owns lower corrosion to quartz tube. The experimental effect of flow ratio of NH3 to HCl(R) on the morphology and crystallinity of AlN films was analyzed with the source temperature of 800～900 K, growth area temperature of 1 373 K, and HCl flow of 25 cm3/min. AlN single crystal with smooth surface and thickness of 7 μm is obtained under the R ratio of 0.5.