Complement system is an essential part of the innate immunity which serves as a bridge between innate and adaptive immunity. The complement system comprises of over 30 different proteins, most of which are glycoproteins. The recent researches have shown that complement system plays important roles in defense against the evading microbes and maintaining the cellular hemostasis. However, the complement system requires firm controls. Either insufficient activation or over-activation of complement would cause diseases. In this review, we summarize the recent advances in understanding the activation, regulation and the function of complement system and for the first time review the complement system by its glycosylation: we summarize the glycan structures of the complement proteins and analyze the glycosylation impact on the function of the proteins.