Abstract: In order to study the properties of AlGaN/GaN heterostructure grown on sapphire substrate by MOCVD system. Firstly, Al_0.30Ga_0.70N/GaN heterostructures materials were grown on the u-GaN template with the nucleation temperature of 580 ℃ and 600 ℃. Samples are characterized by Optical microscope and HRXRD measurement. Experimental results show that the Al_0.30Ga_0.70N/GaN heterostructures was grown on the u-GaN template with the nucleation temperature of 600 ℃ has better performance Compared with the nucleation temperature of 580 ℃. The surface morphology of the sample is better, and the amplitude of the reflectance curve of GaN epitaxial layer detected in situ is more uniform. The HRXRD measurement results show that the FWHM of the (002) and (102) plane are small (178 rad·s^-1 and 214 rad·s^-1, respectively), and the dislocation density is at a low level (the screw dislocation density is 6.24×10⁷ cm^-2 and the edge dislocation density is 4.1×10⁸ cm^-2). The influence of AlN interlayer layer was studied in order to further improve the performance of Al_0.30Ga_0.70N/GaN heterostructure. Experimental results show that the 2DEG density of Al_0.30Ga_0.70N/AlN/GaN heterostructure increases obviously and at a high level, that is 3.014×10¹³ cm^-2. Meanwhile, Al_0.30Ga_0.70N/AlN/GaN heterostructure with AlN interlayer displayed the average sheet resistance of 277.0 Ω less than 331.9 Ω of without AlN interlayer obviously. The above results show that optimizing the temperature of the nucleation layer and introducing the insertion layer are effective methods to improve the Al_0.30Ga_0.70N/GaN heterostructure performance.