Abstract: The pressure of tritium gas as a function of time during it was being absorbed either by 5.9 year aged palladium powder with helium-to-palladium atomic ratio 0.199 or by fresh palladium powder was experimentally measured for initial pressure 350kPa tritium gas. Mechanism of palladium tritium absorption and aging effects on palladium tritium absorption rate were analysed. The results indicate that the tritium absorption pressure of fresh palladium decreases rapidly in 5s and the tritium absorption pressure of 5.9-year-aged Pd of which the atomic ratio to He is 0.199 decreases slowly. The atomic ratio of tritium and palladium of fresh palladium reaches to 0.3 in 5s, and the atomic ratio of tritium and palladium of aged palladium is just 0.07. The tritium absorption rate of fresh palladium maxes out to 0.11/s in 2s, and falls down rapidly to 0.02/s in 6s. The tritium absorption rate of aged palladium reaches to maximum value at 0.02/s in 1s, and then falls down slowly. The tritium absorption rate of fresh palladium maxes out at α+β-phase, and the tritium absorption rate of aged palladium at α-phase. The ³He that emerges from the decay of tritium blocks the diffusion of tritium and influences the tritium absorption rate.