Polylactic acid (PLA) is a kind of polymer material fully degradable with good mechanical properties and broad application prospects. But for the traditional polylactic acid, its heat resistance and toughness are poor, the barrier also has some limitations. Therefore, it is necessary to modify it physically and chemically to meet the requirements of application environment. The preparation of monomer of lactic acid and the synthesis method of polylactic acid were introduced. The basic properties, barrier and degradation properties of polylactic acid, as well as its application in packaging industry, agricultural production and medical industry were reviewed. The modification methods and effects of polylactic acid were analyzed. Finally, the research direction and application prospect of PLA were prospected.