There are three steps in the advances of the theory on petroleum system: ① Petroleum System, ② Superposite Petroleum System, and ③ Accumulation Petroleum System, which advanced from simpleness to complexity, and a sourcedominated petroleum system to a reservoirdonminated petroleum system. The concepts of Accumulating Petroleum System would give us a more clear description in modality and a more exact place in location about the reservoir in petroleum exploration, and it is a systematized ideology in petroleum geology research, and tell us how to solve the complicated problems about oil and gas generation, migration and accumulation using a systematized method.