Si-based Ge/SiGe type-Ⅰ quantum well is theoretically designed based on the energy band engineering theory.High-quality Ge/ SiGe multiple quantum wells were grown on Si-based germanium virtual substrates by ultra-high vacuum chemical vapor deposition.When the thickness of the Ge quantum well is reduced from 15 nm to 12 nm and 11 nm,the quantum confinement effect in the Ge/SiGe quantum wells can be directly demonstrated by room temperature photoluminescence(PL),which is in good agreement with the theoretical prediction.But when the thickness of the Ge quantum well is gradually reduced to 9 nm and 7 nm,the experimental result doesn′t obey the theoretical prediction.Further experiments reveal the reason that when the thickness of the Ge quantum well is reduced to some extent,the photoluminescence from the direct band transition of the Ge well will be restrained and it mainly originates from the Ge virtual substrate.