Abstract: Combining BLP and BIBA model in a MLS policy will leed to poor availability. To resolve it and enhance the security mechanism in the environment of high level security system, TCPA’s trusted computing platform was applied to construct new security policy named S/IMLS. S/IMLS is based on the mechanism and function provided by TCPA. It defines the concept of trusted subjects by behavior and confines their abilities, which increase simplicity and availability for the system.