Abstract: Using drilling core observation,casting thin sections identification,scanning electron microscopy(SEM)and combining with logging and mud logging data,this study carries out a systematically research on the characteristics of diagenesis,type of diagenetic facies and favorable diagenetic facies of Paleogene Lulehe Formation sandstone in Lenghu region of the northern Qaidam Basin.The results show that reservoir compositional maturity and textural maturity are low,and the reservoir has experienced complicated diagenesis,mainly including compaction,cementation,replacement and dissolution.The reservoir in the study area is mainly at the middle diagentic stage B period.This paper classifies 4diagenetic facies belts,including dense strong compaction diagenetic facies,carbonate cement diagenetic facies,chlorite coat cementation-intergranular pore diagenetic facies,and unstable comoponents dissolution secondary pore diagenetic facies by comparing all kinds of diagenetic phenomena and features,pore types and sedimentary microfacies.The distribution of high quality reservoir has a close relationship with diagenetic facies.The reservoir property of dense strong compaction diagenetic facies and carbonate cement diagenetic facies are generally poor,mostly which are tight sandstones with low permeability mainly distributing in flank of fan delta plain river and the edge of fan delta distributary channel.However,chlorite coat cementation intergranular pore diagenetic facies and unstable comoponents dissolution secondary pore diagenetic facies mainly developing in the thick subaqueous distributary channel,the middle and the upper part in the mouth bar sand body of the fan delta front are enrichment for oil and gas reservoirs and are the favorable diagenetic facies in the study area due to the better reservoir property from primary pore and secondary pore development.