In order to realize the monolithic integration of Ⅲ-V devices on silicon platform, the heteroepitaxy of Ⅲ-V semiconductor on silicon substrate has been widely studied in recent years. Due to the large lattice mismatch and different lattice structure between Ⅲ-V semiconductor and Si, there are many mismatches and antiphase domains in Ⅲ-V semiconductor grown on Si, which have a serious impact on device performance. However, the diatomic steps on Si (111) surface can avoid the formation of antiphase domains. In this work, GaAs (111) films were grown on Si (111) substrate by molecular beam epitaxy, and Al/AlAs was used as intermediate layer for the first time. A series of samples were grown to optimize the growth conditions of Al/AlAs interlayer and it is shown that Al/AlAs interlayers have positive effect on the quality of subsequent GaAs films. On this basis of the Al/AlAs interlayers, the GaAs films were grown by two-step method and the growth conditions were optimized. The results show that Al/AlAs interlayers provide a template for the epitaxial growth of GaAs and release the mismatch strain between GaAs and Si to a certain extent, so that the crystal quality of GaAs films can be improved. All of the above-mentioned work can provide new ideas and pathways for the growth of Ⅲ-V semiconductor on silicon.