Basedonagreatdealofthinsections,cathodoluminescence,electronmicroscopic,corephysicalpropertyandloggingdata,the characteristicsofreservoirandformationmechanismoftheMalluvialfanreservoirinLaojunmiaoOilfield,wasdiscussed,includingthe sedimentarycharacteristicsofreservoir,diagenesisandporosityevolutionwereanalyzed.TheresultsshowthatMreservoirhaverapid accumulation,poorsortingandhighmatrixcontents,itoverallbelongrelativefinealluvialfan.Themainreservoirspaceareintergranular poreswiththecharacteristicsofmediumporosityandlowpermeability.Thedominantdiagenesisinthestudyareahavecompaction, cementationanddenudation.Sedimentationcontrolledtheprimarypores.Thehighmatrixcontentsandpoorsortingresultinthepoorreservoirproperties.ThekindofreservoirisprimarilydistributioninSheetflooddepositionandbraidedriver.Incontrast,thelowmatrix contentsandgoodsortingofthebraided-streambeltreservoirisgreatlyaffectedbycarbonatecement.Carbonatecementfurtherreduce thereservoirphysicalproperties,whichresultinfeaturesoflowpermeableforMreservoir.Thecontentofmatrixandcarbonatecement aremajoraffectingfactorsforlowreservoirphysicalproperty,whichcausethequalitydifferenceanddistributionofreservoir.