The invention relates to the technical field of semiconductor manufacturing and design, and in particular relates to a GaAs/Si epitaxial material preparation method which comprises the following steps: selecting a single crystal Si substrate, and washing the single crystal Si substrate; forming a concave layer on the single crystal Si substrate; forming an Si film layer on the concave layer, and suspending the Si film layer in the groove of the concave layer; forming a GaAs seed layer on the Si film layer; forming a first GaAs buffer layer on the GaAs seed layer; forming a GaAs second buffer layer on the first GaAs buffer layer; and forming a GaAs epitaxial layer on the second GaAs buffer layer. By adopting the method, the high-quality GaAs crystal film can be prepared on the single crystal Si substrate which is low in price, and moreover an additional stress field is not introduced, so that additional adverse influence on quality of devices can be avoided in later device manufacturing.