For　fluid-filled　closed　cell　composites　widely　distributed　in　nature,　the　configuration　evolution　and　effective　elastic　properties　are　investigated　using　a　micromechanical　model　and　a　multiscale　homogenization　theory,　in　which　the　effect　of　initial　fluid　pressure　is　considered.　Based　on　the　configuration　evolution　of　the　composite,　we　present　a　novel　micromechanics　model　to　examine　the　interactions　between　the　initial　fluid　pressure　and　the　macroscopic　elasticity　of　the　material.　In　this　model,　the　initial　fluid　pressure　of　the　closed　cells　and　the　corresponding　configuration　can　be　produced　by　applying　an　eigenstrain　at　the　introduced　fictitious　stress-free　configuration,　and　the　pressure-induced　initial　microscopic　strain　is　derived.　Through　a　configuration　analysis,　we　find　the　initial　fluid　pressure　has　a　prominent　effect　on　the　effective　elastic　properties　of　freestanding　materials　containing　pressurized　fluid　pores,　and　a　new　explicit　expression　of　effective　moduli　is　then　given　in　terms　of　the　initial　fluid　pressure.　Meanwhile,　the　classical　multiscale　homogenization　theory　for　calculating　the　effective　moduli　of　a　periodical　heterogeneous　material　is　generalized　to　include　the　pressurized　fluid　＂inclusion＂　effect.　Considering　the　coupling　between　matrix　deformation　and　fluid　pressure　in　closed　cells,　the　multiscale　homogenization　method　is　utilized　to　numerically　determine　the　macroscopic　elastic　properties　of　such　composites　at　the　unit　cell　level　with　specific　boundary　conditions.　The　present　micromechanical　model　and　multiscale　homogenization　method　are　illustrated　by　several　numerical　examples　for　validation　purposes,　and　good　agreements　are　achieved.　The　results　show　that　the　initial　pressure　of　the　fluid　phase　can　strengthen　overall　effective　bulk　modulus　but　has　no　contribution　to　the　shear　modulus　of　fluid-filled　closed　cell　composites.