The recovery behavior of quenched-in or radiation-induced defects in the intermetallic compound NiAl has been studied by positron annihilation techniques.Two distinct recovery stages in NiAl samples quenched from temperature above 950℃ were found by Doppler broadening measurements;one at around 280℃and the other at around 500℃.The molecular dynamics was then further used to simulate mono-vacancies and divacancies in the NiAl of stoichiometric composition with"embedded atom method"（EAM） potentials. The vacancy ingration energies for three different mechanisms were calculated. The calculations indicated that the energetically favorable mechanism for vacancy migration was six-jump vacancy cycle.A comparison with the experiments showed that Al vacancies annealed out at the～280℃recovery stage while Ni vacancies at the～500℃ stage

and the vast majority of diffusion events in the ordered NiAl alloy were mainly attributed to the motion of vacancies.