In network system, network coding allows intermediate nodes to encode the received messages before forwarding them, thus network coding is vulnerable to pollution attacks. Besides, the attacks are amplified by the network coding process with the result that the whole network maybe pollutes. In this paper, we proposed a novel unconditionally secure authentication code for multi-source network coding, which is robust against pollution attacks. For the authentication scheme based on theoretic strength, it is robust against those attackers that have unlimited computational resources, and the intermediate nodes therein can verify the integrity and origin of the encoded messages received without having to decode them, and the receiver nodes can check them out and discard the messages that fail the verification. By this way, the pollution is canceled out before reaching the destinations.