Abstract: Based on the comprehensive application of the data on formation test, core analysis and logging interpretation, the low limits of physical properties of effective sandy conglomerate reservoirs in the Lower Triassic Baikouquan formation of the northern slope of Mahu sag are determined by using the distribution function curve method and formation test method, and regression analysis method is used to match the lower limits of physical properties with depth. Based on which, lithofacies, sedimentary microfacies and diagenesis are analyzed by using the differences of reservoir physical properties. The results show that the lower limits of effective reservoir physical properties exhibit a trend of gradual decrease with the increase of depth in the study area; the development of effective reservoirs is mainly controlled by sedimentary microfacies and lithofacies, and weakly influenced by diagenesis. Microfacies of underwater distributary channel and braided channel are the most favorable areas for effective reservoir development, and tabular cross?bedding and trough cross?bedding are the most favorable lithofacies for effective reservoir development; the sandy conglomerate in the study area is mainly in the A stage of the middle diagenetic period, the secondary pores result from feldspar dissolved by organic acid which is liberated from thermal evolution of organic matter, which can improve reservoir physical properties, the effective reservoirs with the diagenetic faices of weak?compaction?weak?corrosion and unstable component corrosion are the most developed