The invention provides a network authentication method and system. The network authentication method comprises the following steps that: a cloud AC establishes a roaming group and divides an AP in the same roaming group in the same two-layer multicast domain; therefore, when a site sends an authentication request to a target AP, whether a local authentication list of the target AP contains associated authentication information of the AP in the roaming group, where the target AP is, and the site or not can be judged at first; and the site passes authentication when the local authentication list of the target AP contains the associated authentication information of the AP in the roaming group, where the target AP is, and the site. Due to the network authentication method, when the cloud AC and the AP are in different local area networks, the public-network-across authentication request process is reduced; the authentication efficiency is increased; and non-inductive authentication of the site is realized.