Modern information believes that dental caries starts from plaque. Therefore, understanding the formation of dental plaque has important clinical significance for the prevention of caries. The formation of dental plaque is more complicated, and now the recognized theory has the following three stages: 1. Acquired film formation stage: Salivary glycoprotein in the oral cavity is a substance in saliva, and every person’s saliva contains this substance. When it comes in contact with the teeth, it can adhere to the enamel surface and form a film-like substance, and this film is called the acquired film. It provides the substrate for the initial adhesion of oral bacteria and creates the conditions for the formation of dental plaque. Some data prove that the gingival sulcus is the first part of the tooth to form the acquired film. 2. Bacterial attachment stage: Most researchers believe that the acquired film is important for bacterial attachment. It was observed that when the acquired film was formed on the tooth surface, bacteria attached to it very quickly, indicating a rapid rate of attachment. Numerous research data confirmed that the first bacteria to attach to the tooth surface were Streptococcus haematobium and Streptococcus salivarius. The bacteria grow on the surface of the acquired film and are able to produce acid and make glycoprotein deposits. Blood-type Streptococcus and Streptococcus pyogenes can synthesize dextran, which together with the deposited glycoproteins constitute the plaque matrix and create the basis for the formation of dental plaque. 3, plaque maturation stage: bacteria grow, develop, reproduce and decay on the acquired membrane, and carry out complex metabolic activities in it. According to the analysis of relevant data, the proportion of bacteria in the mature dental plaque is: 27% of parthenogenic anaerobic streptococci, 23% of parthenogenic class diphtheria bacilli, 18% of anaerobic class diphtheria bacilli, 13% of peptostreptococci, 6% of Weyong’s bacilli, 4% of anthropoid bacilli, 4% of clostridia, 3% of Neisseria, 2% of vibrios. The cariogenic bacteria in mature dental plaque were Streptococcus pyogenes, Streptococcus radiodurans, Streptococcus haematobium and Lactobacillus.