As a bio-based biodegradable polymer material, polylactic acid (PLA) has a wide range of sources and good processing property. However, its low strength and toughness limit its application in many fields. In recent years, people have developed a variety of methods to reinforce and toughen PLA to obtain better performance. Herein, combined with our work, this review focused on the research advances in the reinforcing and toughening of PLA in recent years. First, the reinforcing and toughening mechanisms of PLA were introduced. Based on these, the strengthening and toughening methods of PLA were introduced from chemical and physical modification methods. Then the composites composed of PLA with biodegradable and non-biodegradable polymers were discussed. Moreover, this work summarized the applications of PLA in green electronic devices, biomedicine, bio-based shape memory polymers and other fields. Finally, the future developments and challenges of PLA were also discussed. This review aimed to provide directions and ideas for the development of new reinforcement and toughening methods.