Cytidine is an important intermediate for antitumor or antiviral drugs. Traditional method for screening of cytidine producing strain was generally based on physical or chemical mutation combined with resistance screening method of metabolic product analogues to obtain high yield strain. With the development of molecular biology technology, the yield or quality of target product can be effectively improved by gene knockout technology to block cell metabolic pathways or introduce mutant site. In this study, the biosynthetic pathways of cytidine in B. subtilis and E. coli were analyzed, and the breeding strategy for cytidine production strain was reviewed.