Marine shale of the Paleozoic Erathem Longmaxi Formation and Qiongzhusi Formation in Southern China is deeply buried. Having been through a complex history of tectonic transformation, the shale is highly mature and it has a significant impact on the capacity of shale reservoir as well as the gas saturation. To ascertain the characteristics and enrichment rules of marine shale gas reservoir in southern China, we analyzed the evolution of the reservoir formation and studied the fluid inclusion. In this paper we found that the Himalayan tectonic movement in southern China has a critical impact on the evolution of shale gas reservoirs, which is reflected in an abnormal formation pressure coefficient. This causes the phenomenon of ultra-low water saturation and the formation of an overpressure core area. In this paper, the distribution range of the southern marine shale can be divided into the basin-interior stable region, basin-edge transition region and the basin-exterior active region. We experimented to analyze the water saturation, relative permeability and fluid inclusion using samples at the southern marine Longmaxi formation. The final phase of the intense Himalayan tectonic uplift has a significant impact on the shale gas reservoir, and it thereby affects the enrichment of shale gas. A part of the shale suffers from an ultra-high water saturation, which would cause damage to the shale gas. This paper believes that the formation pressure coefficient and dip angle are two important metrics in characterizing the condition of shale preservation. The overpressure geological condition and dip angle are proposed as the major measurements in selecting the overpressure core. Tectonic uplift and ultra-low water saturation are considered to be the reason why overpressure shale gas enrichment zone develops in tectonically stable areas in southern China. The overpressure shale gas reservoirs are widespread in overpressure cores, which is the major target for exploration.