Abstract: How to bind secure label to data object is a key problem in multi-level network that restricts MLS from practicality on network．This paper analyzed deeply xml,and expounded secure label of object based on xml and its restrictions,then put forward a method of binding secure label to data object based on XML．At the same time,some operations were discussed in detail,such as query of secure label,decomposition of object．Finally,secure communication based on secure label was described in multi-level network．The method can not only meet the need of secure communication in multi-level network,but also accomplish fine-grained mandatory access control,which may improve availability of information and reduce complexity of binding．

Key words: MLS,Classified security protection,XML,Secure label,Data object