Abstract: The shallow layer of the Wenchang B depression in the western part of the Pearl River Mouth Basin has a high exploration degree. Currently, the middle and deep layers of Enping and Wenchang formations are the key exploration layers. In recent years, multiple exploration wells in the X area of this depression have achieved good oil and gas discoveries in the middle and deep layers, but the formation mechanism and distribution pattern of high-quality reservoirs have not been clearly studied, which restricts the achievement of a breakthrough in oil and gas exploration in the middle and deep layers of the X area. To address these issues, comprehensive use of logging, core, cuttings, petrographic thin sections, and fluid inclusions analysis data from the study area, through the "three-line combination" method, determined the middle and deep layer high-quality reservoirs, and explored their evolution process and formation mechanism. The research results show: ① The pore development of the middle and deep layer high-quality reservoirs in the X area is mainly controlled by organic acid dissolution for pore enlargement and oil and gas injection for pore preservation; ② The subaqueous distributary channel deposits at the front edge of the fan delta provide rich material sources for the development of the X area's high-quality reservoirs. The inhibition of compaction and cementation by hydrocarbon injection is the key factor for the formation of high-quality reservoirs, and the early carbonate cementation prevented large-scale carbonate cementation in the middle and deep layers. At the same time, affected by organic acid dissolution and closed-type formation water environment, the middle and deep layers mainly have secondary solonoclastic pores of the blending type. ③ The "deposition - diagenesis - oil injection" multi-factor comprehensive analysis was used to predict the planar distribution range of the high-quality reservoirs in this area. It is believed that thick fan delta front thick sand bodies adjacent to source rocks or close to oil source faults and far from volcanic rock bases are the key development areas of high-quality reservoirs.