The Southern Lufeng Sag is endowed with abundant deep hydrocarbon resources, while low reservoir permeability and strong heterogeneity constitute the key factors restricting efficient hydrocarbon exploration in this area. In this study, a variety of experimental methods were employed, including core analysis, SEM, thin-section ,XRD, physical property tests, and zircon dating, to investigate reservoir characteristics, main controlling factors, and sweet spots mechanisms.Results indicate that reservoirs are dominated by feldspathic and lithic quartz sandstones, with well-developed pores, while their permeability shows significant variations: low-permeability to ultra-low-permeability reservoirs are concentrated in the Huilu Uplift area. The parent rocks of the Wenchang Formation are dominated by sedimentary rocks. Volcanic ash from synsedimentary volcanic eruptions is a key factor contributing to the generally low permeability of the reservoir. Sedimentary environment, volcanic ash, and tectonic modification play important roles in controlling the differential evolution of deep low-permeability reservoirs in the southern Lufeng area. Effective reservoirs are formed in high-hydrodynamic environments and undergo late-stage karstification or tectonic fracture modification, resulting in well-connected pores. Five types of low-permeability reservoirs have developed in the study area. Among them, Type I/II reservoirs are sweet spots, and commercial productivity has been achieved through the improvement of testing technologies; Type III reservoirs have the potential for productivity release, while Type IV-V reservoirs are currently difficult to develop and produce.