The influenza virus hemagglutinin(HA) is a potential drug target for anti-virus treatment.A variety of membrane fusion inhibitors targeting HA were discovered but the binding sites and the binding modes of these inhibitors,which is important for rational drug design and understanding the mechanism of membrane fusion,are not fully clarified.In this paper,we investigated the possible HA binding sites of the current membrane-fusion inhibitors targeting HA.Five possible binding pockets(Pocket A,B,C and D) at the stalk region of HA2 were detected and defined by using our CAVITY program.Most of the membrane-fusion inhibitors were believed to bind in Pocket C according to amino acid mutation experiments with molecular modeling.