The present invention provides a MOCAD preparation method of GaAs/Si epitaxial materials. The MOCAD preparation method comprises: manufacturing a GaAs low-temperature nucleating layer on a clean single silicon substrate; manufacturing a GaAs middle-temperature buffer layer on the GaAs low-temperature nucleating layer; manufacturing a GaAs first high-temperature buffer layer on the GaAs middle-temperature buffer layer; manufacturing a GaAs second high-temperature buffer layer on the GaAs first high-temperature buffer layer; manufacturing a GaAs temperature-variable buffer layer on the GaAs second high-temperature buffer layer; manufacturing layers of quantum dot dislocation barrier layers on the GaAs temperature-variable buffer layer; manufacturing a strain insertion layer on the layers of quantum dot dislocation barrier layers; manufacturing a GaAs epitaxial layer on the strain insertion layer. According to the invention, the growth and the preparation of materials may be uniformly completed with high repeatability on a large area, and the dislocation density of the growing materials is reduced, so that the cost is lower and the MOCAD preparation method of GaAs/Si epitaxial materials is more suitable for the industrial requirement.