Polylactic acid (PLA) when combined with 3D-printing technology has been used in various fields owing to its excellent biodegradability. However, the application of PLA as a 3D-printing material is limited by several characteristics, such as its fragility with a poor impact resistance and poor dimensional stability. Recently, PLA has been processed to improve its properties and retain its biodegradable advantages, thus significantly enhancing the performance of PLA materials in several aspects, such as their mechanical properties, printability, print quality, and functionalization. This paper specifically focuses on PLA in 3D printing and reviews the latest processing methods of 3D-printed PLA developed in the last three years, including physical, chemical, and chemical/physical composite processing methods. It also introduces the processing methods and results of PLA in different extrusion stages, as well as its print quality and application in various printing processes. Finally, it reviews the functional processing of products in terms of applications. This review provides reliable data for further research on PLA, which can be used as a reference for the practical application and production of PLA and MEX. Display omitted