Abstract: Imbricated reservoir is the main reservoir type in Xinzhuang oilfield. The forming conditions of reservoirs are discussed in respects of the effectiveness of traps and seals. It is concluded that the main faults are extensive but relative seals of oil zones, thus most of the reservoirs in the high side of the footwalls are oil- bearing, oil columns, however, are low. The thickness of seals is proportionate to the height of oil column.