Abstract: The dynamic changes of pH, reducing sugar, total sugar, alcohol content, total acid and the total number of colonies, acetic acid bacteria, lactic acid bacteria and yeast on the surface and in the vinegar liquor during the fermentation of Laocang vinegar were systematically analyzed. The results showed that the content change of every physical and chemical index was closely related to the change of microbial phase, and influenced each other. According to the changes of physio-chemical indices and microbes, the process of fermentation could be divided into three periods: from 1st to 13rd was alcohol fermentation stage; from 13rd to 25th was acetic fermentation stage; after 25 days was ripening stage. Information for production quality control was provided, as well as shortening fermentation cycle and product development, which would be helpful for screening functional microorganisms that meet the needs of each fermentation stage.