Abstract: At present, conventional petroleum explorations have become more and more difficult. On the contrary,unconventional petroleum reservoirs represented by nano-meter oil and gas have a great potential, and are the main fields for petroleum explorations. Due to the obvious differences between conventional and unconventional petroleum, traditional petroleum geology which was used to guide conventional petroleum explorations is no longer suitable for unconventional petroleum explorations. Nano-meter petroleum geology is an interdiscipline between nanotechnology and petroleum geology. It came into being due to the demands of unconventional petroleum explorations and the booming of nanotechnology. The mechanisms and laws of nano-meter petroleum generation, retention, migration, accumulation, preservation and escaping are the main research tasks of nano-meter petro-leum geology. The forming, output states and distribution features of unconventional petroleum are the main aims of nan-meter petroleum geology. Nanotechnological idea and its high-resolution testing techniques, physical simulation experiments, typical example analyses are the main guiding thought and research measures. As a new petroleum geology theory system, nano-meter petroleum geology will play an important role in future petroleum exploration and development.