The innate immunity of invertebrate is one of the focuses of current research. The results show that fibrinogen-related proteins (FREPs) play an important role in invertebrates immune defense, which is considered one of the most important molecule to participate in immune defense. This article introduces the latest research on FREPs from three aspects, namely molecular structure, molecular polymorphisms and function. This will provide a theoretical basis to understand the innate immune mechanisms of invertebrates and co-evolution in host and parasites.