The microbial and physicochemical indexes of different fermentation stage were determined， and the dynamic changes of microbial and physiochemical indexes in the fermentation process were discussed. The results showed that the functional microorganismsg the brewing process of mild flavour Baijiu were mainly yeast and baterial. The temperature changes were‘slow forward， moderate， slow down’. The pH value showed a trend of decreasing graduallyhe in the fermentation process. The starting pH value of Dacha fermentation was higher than the starting pH value of Ercha fermentation. The pH value was approximately 3.3. The content of alcohol increased gradually and then became stable after 15 days of fermentation. The content of water did not change dramatically after 23 days of fermentation. The change trend of starch content in the fermenting process of Dacha was decreased first and remained stable gradually. The change trend of starch content in the fermenting process of ercha was decreased gradually. The reducing sugar content was fluctuated dynamically in fermented grains， but the content of reducing sugar remained lower in the later fermentation period. The change trend of starch content and reducing sugar content were beneficial to improve the quality and ensure the yield of mild flavour Baijiu. The research above would lay the theoretical basis for the regulation of fermentation of mild flavour Baijiu.