To address the issues of strong heterogeneity in the 4th member of the Dengying Formation reservoir in the Sichuan Basin and insufficient constraints for reservoir prediction using subsurface data, a well-exposed (algae) mound-shoal complexes profile of the 4th member of the Dengying Formation in Ningqiang area, northern margin of the Sichuan Basin is selected as a field prototype model. Based on detailed field surveying, sampling, and rock thin section analysis, this study establishes a dolomite reservoir model and defines the spatial relationship between reservoir parameters and lithofacies architecture. The following insights are obtained: (1) The 4th member of the Dengying Formation in Ningqiang area can be divided into lower, middle, and upper sub-members, forming a shallowing-upward cycle from middle ramp to weakly rimmed platform margin to strongly rimmed platform margin. The main rock types are microbial dolomite and crystalline dolomite, with microbial dolomite being the dominant type, including algal peloidal dolomite, algal stromatolite dolomite, algal laminated dolomite, algal framework dolomite, and algal thrombolite dolomite. The upper sub-member develops typical platform-margin (algae) mound-shoal complexes, in which algal framework dolomite, algal stromatolite dolomite, and algal thrombolite dolomite have porosity > 4.5%; algal peloidal dolomite and fine-crystalline dolomite have porosity between 2.5% and 3.5%. Toward the interior of the platform, algal laminated dolomite, very fine-muddy crystalline dolomite have porosity < 2.5%. (2) The reservoir spaces in algal framework dolomite and algal thrombolite dolomite are characterized by large pores and throats; those in algal stromatolite dolomite, algal peloidal dolomite and fine-crystalline dolomite are characterized by medium-sized pores and throats; and those in algal laminated dolomite, very fine-muddy crystalline dolomite are characterized by small pores and throats, exhibiting a dual pore-throat structure. (3) The stacking pattern of the lithofacies is clear: algal peloidal dolomite and fine-crystalline dolomite represent clastic shoal deposits in the mound base and inter-mound areas; algal stromatolite dolomite represents deposits during the colonization stage of microbial mounds above the mound base; algal framework dolomite represents mound core construction; and algal thrombolite dolomite represents mound-flank deposits, exhibiting a "small mound, large shoal" pattern. These results indicate that the platform-margin mound-shoal complex in the upper sub-member of the 4th member of the Dengying Formation in northern Sichuan Basin is extensively developed, representing a favorable zone for high-quality reservoir development.