Abstract: Metacommunities are structured and maintained by a combination of local and regional processes. In monsoon region, the temporal dynamics of hydrological factors have important influences on stream metacommunity structures and structuring. Based on the theoretical framework of metacommunity, taking stream benthic diatoms as research objects, 12 sites in Xiangxi River were investigated from September 2004 to September 2006, the space-time interaction model, elements of metacommunity structure, and variation partitioning were used to analyze the temporal dynamics of the metacommunity structure and structuring processes, and through regression analyses, the relationship between the temporal dynamics of metacommunities and hydrological factors were explored. The results showed that the structures and structuring of stream metacommunity have obvious temporal dynamics. During the dry season and the normal season, the metacommunities presented nested structure, under the influences of dispersal limitation and environmental sorting processes, respectively. The high rate dispersal produced mass effect, which made metacommunity structures similar to Clementsian or Gleasonian. Floods played important roles in structuring stream metacommunity. The maximum flow within 7 days (Q7-max), and the time since three times the median discharge (Reset time) had significant negative impacts on the relative importance of spatial factors in metacommunity structuring. The reset time and the metacommunity structures showed a slightly significant binomial relationship, the metacommunity began to recover from 75 days after the flood.