High-quality tensile strained Ge layer was epitaxially growth on a Si(100) substrate by low-and hightemperature two-step growth method in ultrahigh vacuum chemical vapor deposition. The FWHM of double crystal X-ray diffraction is only 537 arc sec. The photoluminescence peak in the wavelength range expands to 1560 nm due to the 0.2% tensile strain in the Ge layer. The results indicated the Ge layer is one of the promising materials for Si-based light emitting devices.