Abstract: According to physical property analysis, mercury injection, cast section SEM and X-ray diffractions，the authors studied the diagenetic features of Chang 6 reservoir in the Zhiluo oilfield of northern Shaanxi, and have reached the conclusion that Chang 6 reservoir belongs to the "A" stage of late diagenesis. The impact and consolidated filling have destroyed the porosity of the sandstones. Carbonate, hydrosyalite and quartz-feldspar overgrowths were the main cements that reduced the reservoir quality of the sandstones. Thin chlorite film around detrital grains prevented overgrowth of part of quartz and feldspar and precipitation of carbonate cements, thus preserving a part of primary pores. Dissolution produced secondary pores and improved the physical property. Four kinds of diagenetic facies were recognized in the study area. There exists intimate relationship between qualified reservoirs and diagenetic facies: the physical properties of secondary pore diagenetic facies are the best, followed by chlorite cementation facies. These facies constitute the favorable diagenetic facies for the reservoir development.