The invention provides a safety method in a multi-access network. A first router receives new address session adding request messages, a legal address of a host to be added in a session is inquired according to preset session legal address table entry information, the legal address of the host to be added is inquired to find out the legality of an address to be added of the host to be added, and whether the address to be added is added into the session or not is determined according to the inquiry result. By the adoption of the safety method in the multi-access network, the phenomena that an attacker utilizes a false address to launch flooding attacks and the attacker pretends to be a legal host to launch hijacked attacks can be avoided.