Peptidoglycan (PG) is a class of microbial polysaccharides with the functions of immunomodulation, anti-tumor, anti-inflammation, adsorption and toxicity reduction, which mainly exists in the bacterial cell wall. Due to its unique biological functions and structural properties, it has attracted much attention in scientific research and practical applications, and is now widely used in many fields such as medical, aquatic, and food. This paper summarizes the research progress of peptidoglycan in terms of its structure, biosynthetic pathway, extraction, function and application. In terms of extraction, the traditional physical and chemical methods, enzyme digestion and the emerging combined extraction method are described, and the advantages and disadvantages of each method are analyzed. The potential link between the biological functions of peptidoglycan and bacterial pathogenicity and immunomodulation is explored in depth. The results and challenges in practical applications are discussed, and the broad prospects of peptidoglycan research in multiple fields are envisioned for the future. By reviewing the current status of peptidoglycan research from multiple perspectives, it provides a reference for the subsequent in-depth study of its properties and the expansion of its applications.