Network coding technology has obvious advantages for improving networks throughput,balancing network load,improving bandwidth availability ratio, enhancing robustness of networks, but it can't resist against pollution attacks directly. Recently, scholars propose the signature scheme based on homomorphic Hash function, which could better detect pollution attacks, but it is difficult to locate the contaminated node. This paper proposes a network coding scheme based on the digital signature by combining with the advantages of both. It can not only resist pollution attack, but also can effectively identify position of attack source. Thus, it reduces the impact of pollution attacks to the network and enhances the robustness of the network.