Abstract: Chang 6 oil group at Xinghe area in Ordos basin prima-rily is at the deltaic front subfacies,and its reservoir rocks consist of the sandstones of underwater distributary chan-nels,distributary mouth bar,delta front sheet sand deposit.Reservoir rocks at Xinghe area in Ansai oilfield are mainly composed of arkose and lithic arkose.Form the data of core analysis,casting thin-section,scanning electron micro-scope,the normal physical properties analysis,mercury in-jection test and logging,it is revealed that the pore space of reservoir mainly includes the primary residual intergranular pores and the secondary pores,of which the secondary pores in most parts are zeolite and feldspar-dissolved pores with a small amount as lithic-dissolved pores,so the sandstone reservoir is characterized by low permeability and porosity,high displacement and saturation median point pressure,small pore throat radius,poor pores throat sorting.Dissolu-tion for pore throat connectedness does not improve obvious-ly,so the pore structure parameters are poor in accumulation properties.The sandbodies of underwater distributary chan-nels sedimentary microfacies deposit are the main reservoir at Chang 6 area,and the distributary mouth bar sedimentary microfacies are next,and delta front sheet sand sedimentary microfacies the third.