Abstract: By using core data,casting thin section and scanning electron microscope,the diagenesis and favorable diagenetic facies of the Chang 6 reservoir in the Jiyuan area were comprehensively analyzed.The results indicate the compaction is the main factor leading to the decrease of the primary porosity in Chang 6 sandstone,and the dissolution pores formed by the dissolution of the feldspar and other soluble minerals are effective to improve the reservoir physical properties.Chang 6 sandstone is in the late stage of middle diagenesis phase,and the late chlorophyll film in the early diagenetic period has a positive effect on the preservation of the primary porosity.According to the diagenesis and sedimentary characteristics,five diagenetic facies zones were classified.The diagenetic facies belt of feldspar corrosion and chlorite film-intergranular pore are the most favorable diagenetic facies in the study area,which are mainly distributed in distributary channel of ShayaoxianZhangjiashan and Majiashan-Fengdikeng areas.