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This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy, metal impurity, impurity vacancy complex in LiNH(2), a promising material for hydrogen storage. It finds easy formation of H vacancy in the form of impurity vacancy complex, and the rate-limiting step to the H diffusion. Based on the analysis of the density of states, it finds that the improvement of the dehydrogenating kinetics of LiNH(2) by Ti catalysts and Mg substitution is due to the weak bonding of N-H and the new system metal-like, which makes H atom diffuse easily. The mulliken overlap population analysis shows that H vacancy leads to the H local diffusion, whereas impurity vacancy complexes result from H nonlocal diffusion, which plays a dominant role in the process of dehydrogenation reaction of LiNH(2).