Ultra- deep strata refer to stratigraphic formations that are presently or were once buried at depths over 6 km. The ultra- deep strata of marine formations in China are generally characterized by old age and high maturation, and had experienced numerous tectonic movements. Their unique tectonic, sedimentation and hydrocarbon generation settings determined the complexity of the formation and distribution of hydrocarbon reservoirs in ultra- deep marine strata. The mechanisms of hydrocarbon generation, reservoir formation and accumulation are quite distinct from that of relatively shallow strata, and the exploration is far more challenging than that of the Meso- Cenozoic craton basins abroad. After more than 50 years of exploration, a series of great breakthroughs have been made in ultra- deep oil and gas exploration in central and western China basins, which have significantly elevated the strategic significance of ultra- deep resources. Highlights of the great progress has also been made in our theoretical understandings on ultra- deep geology in China include: ① tectonic activities during major geological transition period controlled the development of geological factors in ultra- deep reservoirs; ② deep- burial at high temperatures led to multiple natural gas generation pathways; ③ sedimentary and tectonic processes determined the formation and preservation of ultra- deep reservoirs; ④ temperature and pressure in ultra- deep petroleum system controlled the petroleum phase evolution, multi- stage accumulation and multi- layer distribution of hydrocarbon in reservoirs, etc. These insights have significantly improved the model of hydrocarbon generation and accumulation previously proposed by foreign scholars based on Meso- Cenozoic marine strata, and greatly expanded the temporal and spatial boundaries for the formation and distribution of hydrocarbon resources in deep marine strata.