Abstract: Properties of ytterbium absorbing deuterium at pressure less than 0.1 MPa in a vacuum system are studied and the phases of deuterides with various D/Yb atomic ratio are analyzed. Results indicate that there are two kinds of physical absorbed states of gases in Yb and its decomposed peaks present at 50～80 ℃ and 250 ℃, respectively. Yb will absorb deuterium when it exposes to deuterium at 400 ℃ for a long time and D/Yb atomic ratio is related with the exposed time and the most is YbH 2.00. Yb has a fcc structure and a 0= 0.549 2 nm. Results of XRD analysis indicate that there are two kinds of structures in ytterbium deuterides, one is fcc with a 0=0.524 nm, another is orthorhombic structure and a 0=0.588 nm, b 0=0.358 nm, c 0=0.678 nm. Crystal cell parameter and volume of fcc Yb will contract when it absorbs deuterium, and contract ratio is 4% and 11%, respectively. Volume contract ratio of orthorhombic ytterbium deuteride is 14%.