This paper discusses the basic features of the Fen-Wei graben system, the North China down-faulted basin, the Paleogene East China marginal sea and the Okinawa marginal sea. According to the block structure, fault block movement and mantle-crust relations, it is proposed that the origin of the graben system and down-faulted basin is due to crustal extension. And according to the oceanic crustal structure, high heat flow and geosynclinal facies deposits, the origin of the marginal sea is considered to be due to the circulation and gushing of partial mantle materials during crustal extension that caused island arcs to be separated laterally. Initially the geosyncline was in a stage of tensional rupture and then compression transformed it into a fold belt. Crustal extension is an important mode of movement of the continental plate. It varies somewhat within the plate and at the plate margins, thus form- ing the graben system, down-faulted basin, marginal sea and island arc. However, these are interrelated and form an integrated whole. Its dynamic source resulted from the concentration of lage amounts of mantle materials and their eastward creeping in the process of meeting and collision of the western part of the Chinese plate and the Indian plate.
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