Thesymmetryenergywhichcharacterizestheisospindependenceoftheequationofstateofasymmetricnuclearmatter,playsacrucialroleinunderstandingavarietyofissuesinnuclearphysicsandastrophysics,suchasheavyioncollisions,exoticnuclei,stabilityofsuperheavynuclei,fusioncrosssections,thestructures,compositionandcoolingofneutronstars[1??5].Muchtheoreticalandexperimentalefforthasbeenmadetoconstrainthedensitydependenceofsymmetryenergy.Uptonow,wehavegotsomebasicknowledgeaboutthesymmetryenergyatlowdensities,whileathighdensitiesweevendonotknowitsvariationtendencyasafunctionofdensity.Theproblemremainsunsolvedduetothedifficultyofnucleon-nucleoninteractionsandmany-bodyproblems.
