Based on the data of abundant wells and core analysis，combined with the characteristics of petrology，diagenesis and reservoir quality，the high-resolution sequence stratigraphic framework of the Baikouquan Formation in Bai21 Block of Baikouquan Oilfield was built through the analysis of single well sequence and sedimentary characteristics. Moreover，the sedimentary characteristics and mechanism of reservoir quality in different orders of base-level cycle were clarified. And then control factors that cause the difference of reservoir quality were discussed. The research results show that：①The hierarchy base-level ascending hemicycles are well developed in the Baikouquan Formation which belongs to a long-term cycle. 3 middle-term cycles and 9 short-term cycles were divided respectively corresponding to 3 sandbeds and 9 layers with in the formation；②The long-term base-level cycles control the alluvial fan distributed in retrogradational stacking pattern.The middle-term base-level cycles control the distribution of sandbodies in the Baikouquan Formation. Fan root subfacies，named B3 member，characterized with massive sandy conglomerated evolves into B2 member characterized with alternative deposition of massive sandy conglomerate and thick-layer fine conglomerate，and finally evolves into isolated braided channel subfacies named B1 member；③The Baikouquan Formation mainly consists of debris conglomerate with high content of plastic minerals and low textural-compositional maturity. Compaction is the main factor caused the loss of porosity. Hydrodynamic forces in the middle of long-term and middle-term base-level cycle tend to be stable and strong，and there are braided channels with low matrix content and strong anti-compaction ability. Therefore，the braided channels in the longterm and middle-term base-level cycle are the best reservoir.