With the emerging applications based on Web Service, end-to-end security becomes more and more important. SSL and current XML security schemas cannot reach the demand of it. This paper proposes a novel security model -- ESM, which integrates some popular XML security schemas and constructs a layered model based on SOAP message transport mechanism. It?s aiming at the end-to-end security issues in Web Service environment. Compared with other security models known to us, this model is more comprehensive and flexible.