The invention discloses a logon system and a method thereof, which relates to information security field. The invention solves the problems that the user can log on Windows by username and password only. In the invention, the Credential Provider module adapted to pop up a human-computer interactive interface when the Credential Provider module is called by the operating system of the computer; further adapted to collect the information needed for logging on the operating system and transfer the collected information to the operating system of the computer; the Cryptographic Service Provider module is adapted to perform authentication with the information received from the operating system of the computer; and, if the authentication is successful, to perform operation with the corresponding private key of the key device logon certificate to generate credential information needed for logging on the operating system. The embodiments of the invention are applied for logging on the Windows, which provide more alternative logon ways for the user.