With　the　use　of　virtualization,　threats　appears　gradually　in　domains　constituted　by　host　and　virtual　machines　(VMs).　Access　control　between　VMs　becomes　a　necessary　method　of　the　security　management　of　virtualized　platform.　The　traditional　Mandatory　Access　Control　(MAC)　based　on　fixed　security　policy　is　greatly　restricted　on　flexibility.　In　this　paper,　we　proposed　a　quantitatively　trust　evaluation　method　based　on　VM＇s　historical　behavior,　which　combined　with　existing　MAC　mechanism,　to　build　a　flexible,　fine-grained　access　control　mechanism.