A network access method and system and a network connection device are provided. A network connection device connected between a first network and a second network obtains first network attribute information about a first network device according to an access request for accessing the second network from the first network device on the first network. The network connection device performs authentication on whether the first network device has a right to access the second network based on the first network attribute information. If the authentication is passed, the network connection device connects the first network device into the second network. If the authentication is not passed, the network connection device prohibits the first network device from accessing the second network.