A lot of research shows that network coding can significantly improve the performance of multi-cast transmission. However, due to the inherent disadvantage of network coding, it is very vulnerable to pollution attacks in which adversaries can inject bogus data. Moreover, those bogus data will be used with legitimate data at the downstream nodes, resulting in the failure of decoding original data as well as a sharp decrease of the network performance. In this paper, we propose a novel approach to identify pollution attacks, so that malicious nodes can be rapidly identified and isolated from the networks. In our scheme, in order to prevent malicious attacks, we design a secure infrastructure in which we exploit key pre-distribution and Message Authentication Codes(MACs), Meanwhile, we propose a secure transmission protocol. Each node registers a key from center server and appends MACs to each packet. Furthermore, in order to make verification, each node needs to carry out hash computation for every incoming packet under the secure transmission protocol. Experimental results demonstrate that our scheme has practical advantages in the presence of end-to-end delay, network throughput and identification delay.