In　an　open　distributed　environment,　protection　of　sensitive　files　and　data　becomes　more　difficult.　Traditional　access　control　mechanisms　are　not　suitable　for　such　dynamic　environment.　Trust　can　be　an　effective　approach　to　solve　the　access　control　problem.　In　this　paper,　by　considering　fuzziness　and　uncertainty　of　trust,　we　propose　a　trust　quantification　algorithm　based　on　grey　fuzzy　comprehensive　evaluation　method.　Then　we　present　an　access　control　model　based　on　trust　quantification.　Simulation　results　show　that　our　mechanism　is　suitable　for　dynamic　access　control　in　distributed　environment.　©　2010　IEEE.