Abstract: Pregnancy-associated glycoprotein（PAG） is a family of aspartate proteases expressed by the placenta of ruminants and synthesized in mononuclear and binucleated cells of the trophectoderm of ruminants. There are a large number of PAG proteins in Bovidae. The protein members of PAG family are different in molecular weight, amino acid sequence and physiological function, etc. A lot of scientific research is needed to reveal the function and role of these proteins. PAG plays an important role in the process of pregnancy in dairy cows. It can be used as a marker to detect pregnancy and diagnose pregnancy loss in dairy cows. It can also be used as an indicator to monitor placental function. This article reviewed the origin of PAG family, its biological function in cattle and its application in bovine pregnancy monitoring, in order to provide theoretical reference for the diagnosis of bovine early pregnancy.