Abstract: The fluctuation of plant community means the seasonal or annual fluctuation of plant commumty but not of its characters caused by the seasonal or annual changes of ecological factors. The fluctuation possesses reversibility and direction. Positive fluctuation makes community advantageous, and negative one disadvantageous. The measuring formula of fluctuation intensity is built as follows: , When FIis positive, it means the positeve fluctuation, and when FIis negative, it means the negative one. The fluctuation of forest community has the following main types: that of growth rate, of hearing fruit and seedling, of seasonal development and of community structure. The fluctuation deffers from that of grassland.

Key words: Plant community, Fluctuation, Fluctuation intensity, Fluctuation type