Abstract: There had been no significant breakthrough in petroleum exploration in Mahu sag of Junggar basin for about 20 years after the discoveries of Mabei oilfield in 1993 and Ma-6 area in 1994. An overall evaluation was conducted regarding the resources, reservoirs and stimulation potential in Mahu sag in the year of 2010. The results showed that the slope area in Mahu sag was the key strategic area for petroleum exploration. Then the exploration idea was changed from the exploration for structures in the fault zones around source to the exploration for lithological reservoirs in the major area within source. Since 2012 more and more discoveries have been achieved successively. Up to now, 6 large reservoir groups have been discovered and 2 large oil provinces have been proved in the south and north, respectively. The incremental OOIP is 12.4×108 t, among which the proved reserves is 5.2×108 t. The discovery of the large conglomerate oil province proves that hydrocarbon could accumulate in the above-source conglomerate reservoirs under the conditions of fracture connecting, and efficient development could be realized in low-permeability conglomerate reservoirs by using fine volume fracturing technology