Variable temperature Hall effect measurement was performed on the AlGaN/AlN/GaN structure with AlN interlayer grown on sapphire by metalorganic chemical vapor deposition. It was measured that the mobility and density of the two dimensionalelectron gas at the interface of AlN/GaN were 1.4×104cm2·V-1·s-1 and 9.3×1012cm-2 at 2K，respectively. Low temperature variable magnetic field measurement manifested that only a single type of carriers contributed to the conductivity in this structure. Quantum Hall effect was observed in field as low as 3T at 2K. The calculated quantum scattering time of 0.23ps is longer than that of AlGaN/GaN structure. This improvement is attributed to the AlN interlayer which effectively reduces the scattering. In addition，further analysis revealed that the small-angle scattering was important in this structure.