Abstract: In the past,security assesment on S-box is concentrated on examining the security of each component function,with little regard for the relationship between these functions.Considering this problem,using the idea of confusion and diffusion presented by shannon on symmetric cryptography,we propose the cross-correlation test indicators of an S-box.An algorithm of cross-correlation test is presented,which evaluates the security of the S-box better.Finally,experiments on the S-boxes of DES and AES were undertaken,and the test results are given.