Abstract: Bacteria are the key group of micro-organisms during the fermentation of Paocai. This study applied the high-throughput sequencing technology to trace the dynamics of Paocai brine bacterial community structures at constant temperature (25 ℃) under airtight microcosm condition. The results showed that there were 10 phyla and 205 genera had been detected within 30 days after the experiment setup. Among them, there were 12 dominant genera which accounted for 94.7%~97.8% of the total OTUs. The sub-dominant were 13 genera and accounted for 2.1%~3.3%. The rare genera were 180 genera and accounted for 0.08%~2.7%. During the 1~7 days after the experiment setup, the community was relatively stable (phase A). From the 8~20 days, the sub-dominant and rare genera were continuously changing (phase B), and on the 8th day, the communities of sub-dominant and rare genera were acutely fluctuated. From 22~30 days, all of the genera changed obviously (phase C). Meanwhile, the Chao1, Ace indices were increasing during 1~30 days, in addition, the Shannon and Simpson indices reached the thresholds during phase C. Therefore, phase A and B, phase B and C had the similar communities, but not the phase A and C, while the pH during the three phases changed correspondingly. The results also showed that at 25 ℃, the dynamics of sub-dominant and rare genera were the key factor which caused the dynamic of the bacterial communities in Paocai brine during the 30 days experiment. In addition, the accumulated effect had been detected, the pH and the bacterial communities havd mutual influences. The optimal preservation time for the Paocai brine was one week under airtight condition at 25 ℃. The functional effects of rare genera from Paocai brine need pay more attentions on.