The Saihantala Sag is one of the main hydrocarbon enrichment sags in Erlian Basin， with an area of 2300 km2 and proved geological reserves of 14580 000 tons. According to  the basic theories of sequence stratigraphy， 5 sequence stratigraphic boundaries were recognized by seismic profile and drilling data， and as a result，the Lower Cretaceous of Saihantala Sag was classified into 4 thirdorder sequences. The systems tracts were subdivided with first flooding surfaces and maximum flooding surfaces  within each stratigraphic sequence and thus the sequence stratigraphic framework was established for the Lower Cretaceous of Saihantala Sag. Reservoirforming factors in different sequences， such as hydrocarbon source and reservoir condition，and so on，were comprehensively analyzed by studies of depositional systems and their evolution， and 3 sets of sourcereservoircap rock assemblages were established in the Lower Cretaceous of Saihantala Sag. The sandbodies of sublacustrine fan and turbidite fan of the LowerMiddle Aershan Formation and middle part of Member 1 of the Tenggeer Formation， which were connected with source rocks in vertical direction，are able to form effective lithologic traps around the oil generating center of Saihantala Sag. Thus they are the most favourable hydrocarbon accumulation zones and the main exploration targets of the Saihantala Sag. 