Pure Ge is grown on Si substrate to control the release of the strain in the heterostructure, which is due to the 4.2% lattice misfit between Ge and Si. In this letter, an innovative approach of multi-buffer layers is proposed for the epitaxial growth of high quality Ge thin films on Si (001) substrates in a molecular beam epitaxy system. The multi-buffer layers, including the low temperature Ge seed layer and the Si-Ge alloy intermediate layer fabricated under different temperatures, serve as defect gathering and annihilating sites to reduce the dislocation density in the top layers. The result reveals that the total thickness of the whole structure is less than 400 nm, with a low threading dislocation density of less than 5×10⁵ cm^-2 in the top layer and a root mean square surface roughness of 1.5 nm.