| The　ranking　of　fuzzy　number　is　an　important　question　which　belong　　to　the　fuzzy　optimization　problem　.In　recent　years　,there　are　many　different　methods　of　ranking　the　fuzzy　number　.Just　basing　on　these　methods　,this　article　propose　the　formula　of　the　satisfaction　degree　of"a ≤b",then　discuss　its　nature　.We　also　deduce　the　expression　of　the　satisfaction　degree　in"a ≤b"　on　the　trapezoidal　fuzzy　number　and　its　geometric　significance　,considering　that　in　this　expression　,the f (α) = α~q or f (α) = (1 -α)~q can　be　thought　as　a　transform　factor　,then　display　the　influence　to　the　α-cut　to　this　fuzzy　number　when　q　varying　,as　well　as　the　influence　to　the　result　of　the　satisfaction　degree　.By　using　the　result　of　the　satisfaction　degree　between　two　fuzzy　numbers,　we　confirm　the　ranking　of　fuzzy　number　by　weight　sum　.This　method　of　ranking　the　fuzzy　number　point　out　that　since　every　elements　in　fuzzy　number　play　different　roles　on　the　question　of　ranking　,we　should　grant　every　element　the　different　weighting　coefficients　according　by　every　element's　different　influence　on　the　result　of　ranking　.It　will　make　the　ranking　more　flexible　and　more　perfect　.We　also　deduce　the　expression　of　the　satisfaction　degree　of　the　triangles　fuzzy　number　and　the　symmetric　triangles　fuzzy　number　and　show　the　method　of　ranking　by　some　examples　.In　the　last　section　,according　to　the　basis　theory　of　rough　set　,we　propose　the　definition　of　an　approximation　space　which　is　basing　on　the　convex　cone　that　contain　the　origin　,and　define　the　upper　and　the　lower　approximation　of　convex　cone　,then　discuss　some　operation　properties.
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