With the wide applicaitons of OAuth2.0 protocol, people have payed a special attention to its security. In order to enhance its security, in this study the digitial signature firstly is introduced, then an improved OAuth2.0 protocol is proposed which has the authentication from authorization server to client and authorization server to resource owner. At the same time based on the Blanchet calculus in computaional model, the correspondence is applied to model the authentication from authorization server to client and authorization server to resource owner, and finally the authentication is proved by CryptoVerif.