To investigate the hydrogen absorption properties of Zr-Nb alloys, the PCT (pressure-composition-temperature) measurements for Zr-Nb alloys with different Nb contents (1wt%~30wt%) were carried out under low pressure in the temperature range of 700~900 oC. The results indicate that the temperature affects significantly the two-phase equilibrium of β-Zr and δ zirconium hydride. β-Zr shows more stable characters than δ zirconium hydride in the system under the high temperature condition. Nb decreases the binding stability between the system and H, and the equilibrium hydrogen content of the zirconium alloy decreases apparently with the Nb content increasing. The main reason for the decreasing of hydrogen absorption is that δ NbH2 with high hydrogen content cannot exist under the condition of low pressure.