An authentication method for a network connection for a network device is provided. An embedded system is installed in the network connection, and the network device is free from a web browser. First, the network device connects to an authentication server, and an internet access request is sent to the authentication server. An authentication page is retrieved from the authentication server. User authentication data is obtained by an input unit of the network device, and then the user authentication data is filled in corresponding fields of the authentication page. The authentication page is transferred to the authentication server. After, when authentication of the authentication page is successful, the network device connects to the Internet via the authentication server.