Abstract: Through studying and analyzing SE-BGP (security enhanced BGP), it was found that it couldn’t validate the cross-alliance AS (autonomous system) and defense the self-launched active attack. To solve the security problems, two-layer cross-alliance hierarchical structure CAHS (cross-alliance hierarchical structure) was designed. Based on CAHS, using the idea of passport visa and the features of AdHASH (additive hash), a cross-alliance BGP security mechanism SCA-BGP (secure crossing alliance for BGP) was proposed. The mechanism has higher security, which is able to effectively validate the identities and behavior authorization of the cross-alliance AS as well as the message carried by them. The experiment results show that SCA-BGP can effectively reduce the certificate scale and extra time overhead to get better scalability and convergence performance.