Mining important persons is significant to network security, especially researches on email network centralization nowadays. To solve the problem that traditional PageRank algorithm is sensitive to the network disturbance, this paper proposes a method which decomposes email network into different layers based on the core number and eliminates the interferential nodes from outer layers. Besides, it improves PageRank algorithm which ranks the nodes quantitatively to find the important nodes. The experiments indicate that it improves the accuracy and reduces the computational complexity in mining important nodes from email network.