Aiming at the vulnerability and security problem of Kerberos protocol, an enhanced scheme of Kerberos protocol based on hybrid cryptosystem is put forward. The aims of the improved scheme are able to defend the password attacks and the insider threads. Public keys and private keys are assigned to the application servers and the AS server, the session key between user and application server is generated by DH key exchanged algorithm. The improved Kerberos protocol is given by six steps and the security is analyzed. Analysis shows that the new scheme can enhance the security of Kerberos and is more efficient than Public key encryption mechanism.