Abstract: As a depot drug delivery system, injectable polylactide-polyglycolide (PLGA) sustained-release microspheres have been successfully used to treat many diseases since the first microsphere product Lupron depot was approved for marketing in the United States in 1989. It has the ability of long-term release in the body for several days to several months, which can not only reduce the times of administration, but also reduce the drug blood concentration fluctuations, significantly improve the safety and patient compliance. In vitro-in vivo correlation (IVIVC) makes the development of microspheres more possible. It can describe the dynamic information of drug release in vivo through the in vitro release behavior of microspheres, and can reduce the workload of each stage and shorten the time span while characterizing the performance of microspheres. IVIVC can provide guidance or support for drug development, production changes, supervision and management. This article summarizes the release mechanism of injectable PLGA sustained-release microspheres, common measurement methods and theories of in vitro and in vivo release. And we also focus on the establishment and application of IVIVC, especially A level IVIVC in the field of microsphere preparations, to provide a reference for further study on in vitro-in vivo correlation of microspheres.