The characteristics of reservoir and its control factors of Es3 member in Area 4，Bonan oilfield were studied using data of core observation and description，casting thin sections，scanning electron microscope and core laboratory analysis.The analysis results show that the reservoir of Es3 member is characterized by low compositional maturity and textural maturity of sandstone，poor physical property and development of secondary dissolution pore，which is controlled by deposition macroscopically and by diagenetic reform microcosmically. The main reason leading to the poor reservoir physical property is compaction，followed by cementation. Dissolution develops well to improve reservoir performance. On the basis of diagenesis study and diagenetic facies analysis，the reservoir diagenetic facies in the study area were divided into 4 types：residual intergranular pore after compaction-unstable component dissolution facies，secondary kaolinite intergranular pore-quartz overgrowth facies，filling and half-filling microfracture-carbonate cementation facies，severe compaction-matrix filling facies. The drilling data in the area reveal that high-quality reservoirs mainly distribute in residual intergranular pore-unsta? ble component dissolution diagenetic facies.