Abstract: Baikouquan formation in the western slope of Mahu sag, Junggar basin is a set of fan-delta sandy conglomerate depositions. High content of igneous rock debris and the big differences among physical properties of reservoir sections always constrain the petroleum exploration in the area. The reservoir characteristics of Baikouquan formation and the controlling factors are studied based on core observation and thin section identification, and the sandy conglomerate reservoirs of Baikouquan formation in the western slope of Mahu sag are re-classified and denominated. Combined with the grain size distribution of cores in the study area and based on the standard GB/T 17412.2—1998 Rock Classification and Naming Scheme: Sedimentary Rock Classification and Naming Scheme, pebble conglomerate is further divided into fine pebble conglomerate and coarse pebble conglomerate. Based on which, moderate grain size of sandy conglomerate, relatively low content of clay minerals and secondary corrosion are considered as the key factors for high-quality reservoir formation