Thick Ge epitaxial layers are grown on Si(001) substrates in the ultra-high vacuum chemical vapor deposition system by using the method of low temperature buffer layer combining strained layer superlattices. The microstructure and the optical properties of the Ge layers are characterized by double crystal X-ray diffraction, HRTEM, AFM and photoluminescence spectroscopy. The root-mean-square surface roughness of the Ge epilayer with a thickness of 880nm is about 0.24 nm and the full-width-at-half maximum of the Ge peak of the XRD profile is about 273. The etch pit density related to threading dislocations is less than 1.5106 cm-2. The direct band transition photoluminescence is observed at room temperature and the photoluminescence peak is located at 1540 nm. It is indicated that the Ge epitaxial layer is of good quality and will be a promising material for Si-based optoelectronic devices