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Based on the 6-s resolution Na lidar measurements during ~395 hours on 47 different nights from May to November 2011 in Beijing(40.2°N, 116°E), China, it was found that the Na density at altitude 83-98 km always exhibited strong short-term fluctuations. The magnitude of the mean absolute increasing and decreasing rates for these short-term fluctuations ranged from ~8 to ~16 cm-3s-1. Their profiles were close to each other with the increasing rate being slightly larger than that of decreasing rate at most altitudes. This difference coincided with the earlier observations that the Na layer column abundance mostly tends to have a slow net increase during night [2]. The characteristic time for the short-term Na density fluctuations had a magnitude ranging from 46 to 118 s at altitudes between 83 and 98 km, which was apparently shorter than the Brunt-Väisälä period (~5 min). The gravity wave seems difficultly to induce observed Na fluctuations.