Abstract: Sourdough is a kind of starter with lactic acid bacteria and yeast as the main flora. It can improve the quality of steamed bread and extend the shelf life on the basis of retaining the original characteristics of steamed bread as a traditional food. In the process of producing steamed bread with sourdough fermentation, microorganisms metabolize to produce acid, alcohol, ester and extracellular polysaccharides and other flavor substances and nutrients, while degrading gluten protein to improve the specific volume and texture characteristics of steamed bread. This paper introduces the fermentation type, main microbial flora and function of sourdough. It analyzes the improvement effect of sourdough fermentation on steamed bread from three aspects: flavor properties, apparent properties and nutritional properties. The current processing technology of fermentation has limitations and other problems, providing theoretical guidance for the industrial production of sourdough steamed bread.