The characteristics of atmospheric-angular-momentum (AAM) and length-of-day (LOD) on diff erent timescales are investigated in this paper, on the basis of the NECP/NCAR reanalysis data and an LOD dataset for 1962-2010. The variation and overall trend of the AAM anomaly (AAMA) at diff erent latitudes are presented, and the relationship between AAMA and LOD is discussed. The AAMAs in diff erent latitude regions exhibit diff erent patterns of variation, and the AAMA in the tropics makes a dominant contribution to the global AAMA. In the tropics, the AAMA propagates poleward to the extratropical regions. It is confi rmed that a downward propagation of the AAMA occurs in the lower stratosphere. Correlation analysis shows that the relationship between AAMA and LOD varies signifi cantly on diff erent timescales. Specifi cally, the tropical AAMA is positively correlated with LOD on short timescales, but they are not obviously correlated on long timescales. This indicates that the interaction between AAM and the earth’s angular momentum follows the conservative restriction on short timescales, but the infl uence of the earth angular momentum on that of the atmosphere depends on the interaction process on long timescales.