In this work, we have successfully grown high quality Al(subscript x)Ga(subscript 1-x)N (400 nm) films with high Al contents (x=0.5) on sapphire (0001) substrates with GaN (150 nm) buffer layers by radio frequency molecular beam epitaxy (RF-MBE). The relationship between the film quality and different Al contents will be discussed in depth. The X-ray diffraction (XRD) 2θ peak of the AlGaN/GaN structure is 34.66 and 35.43 degree with 0.5 aluminum compositions. A degradation of the crystalline quality of AlGaN layers is observed with increasing Al contents. The 6.42 arcmin full-width at the half-maximum (FWHM) of XRD is better than those reported. The 2.985 nm surface roughness for 2μm×2μm area is measured by the atomic force microscopy (AFM).