Temporal-spatial variations of soil NH₄⁺-N and NO₃^--N exists in sand dune fixing process. Contents of soil NH₄⁺-N and NO₃^--N in sand dunes of the Tengger Desert and the Mu Us Sandy Land were measured. Results show that vertically the content of N of either form decreased with the depth along soil profiles; while horizontally，from the top to the slope and the foot of a dune，both increased gradually，but the NH₄⁺-N/NO₃^--N ratio in the depth of 20～40 cm decreased gradually. And their temporal variations were reflected in the succession series of plant community. The content of NH₄⁺-N in the soil increased gradually from the prophase to the metaphase of the series，while the content of NO₃^--N in the soil did from the metaphase to the anaphase of the series. The NH₄⁺-N/NO₃^--N ratio in the depth of 0～20 cm showed a similar trend，while that in the depth of 20～40 cm did not. Such a pattern of temporal-spatial variation of soil NH₄⁺-N and NO₃^--N was reflected in the fixing process of sand dunes，and was a result of the integrated effect of vegetation and environment，and in turn affected plant growth and vegetation dynamics.