Epitaxial Ge films on Si substrates grown by ultrahigh vacuum chemical vapor deposition(UHVCVD) have been characterized by means of high-resolution X ray diffraction(XRD) and Raman scattering techniques in order to investigate the Ge content and residual strain.The results show that the epitaxial film is pure Ge without any Si out-diffusion,but the film is under a small amount of strain.The residual strain leads to the shifts of the diffraction and scattering peaks of the epitaxial Ge films compared with the bulk Ge.The tensile strain due to the difference of thermal expansion coefficients and the compressive strain because of the lattice mismatch are theoretically calculated.The tensile strain increases almost linearly with increasing growth temperature,while the compressive strain decreases inversely with increasing growth thickness.The final strain state of the epitaxial Ge film is determined by these two factors.The measured and simulated strains agree well with each other.