Data secure transmission method among multilevel information systems

The invention provides a data secure transmission method among multilevel information systems. In the method, a regional border gateway of an information system at which a subject is located judges whether security processing is needed according to a security label of the subject contained in an access request; the regional border gateway of the information system at which the subject is located searches whether the corresponding label security channel exists according to the security labels of the subject and an object, if the corresponding label security channel does not exist, a new label security channel is created and the next step is executed, and otherwise, the next step is directly executed; the information in the security label of the subject is written to an IP option field of a data packet of the access request, then the data packet can be forwarded to an information system at which the object is located through the label security channel, and the regional border gateway of the information system receives the data packet via the label security channel; security policies can be compared, if the comparison results are consistent, the data packet can be permitted, and otherwise, the data packet can be abandoned; and when receiving the data packet, the object judges an operation type of the object by the subject and the subject can read or write on the object according to the operation type.