Achieving AlGaN epitaxial layer with high Al content and excellent electrical properties is one of the most important aspects in the preparation of deep ultraviolet optoelectronic devices. In this work, a series of Si-AlxGa1-xN epitaxial layers with high Al content (x＞0.60) were obtained on AlN/sapphire substrates using molecular beam epitaxy (MBE) system, based on the growth method of periodic thermal desorption. Al content was modulated by changing the size of Al source supply, and n-type doping was realized with Si. The physical properties of the epitaxial layers were characterized. The results show that: Al content of the epitaxial layers shows a linear relationship with the Al flux size, which lays the foundation for the growth of AlGaN epitaxial layers with precise content. The AFM measurements reflect that the surface morphology of the AlGaN epitaxial layers strongly depend on the Ga supply. The electrical properties of Si-AlGaN epitaxial layers were measured based on the Vanderbilt method, and the good performance was confirmed. The free electron concentration, electron mobility and resistivity of the sample with Al content of 0.93 reach 8.9×1018 cm-3, 3.8 cm2·V-1·s-1 and 0.18 Ω·cm respectively at room temperature.