Abstract: The study aims to clarify the mechanisms of dolomitization and the differences in reservoir characteristics of the Middle-Upper Cambrian Xixiangchi Formation in the Sichuan Basin. Taking the central and southern Sichuan Basins as research objects, core observations, thin section identification, physical property testing, and geochemical analyses were conducted to systematically investigate their petrological characteristics, reservoir space types, physical property parameters, and dolomitization characteristics. Corresponding reservoir development models were established. The results showed that (1) In terms of petrological characteristics, reservoir rocks of the Xixiangchi Formation in the central Sichuan Basin were dominated by granular dolomite with uniformly sorted crystalline grains, while those in the southern Sichuan Basin were mainly fine crystalline dolomite, locally affected by hydrothermal modification. (2) Reservoir performance differed significantly. Reservoirs in the central Sichuan Basin were dominated by intergranular dissolved pores and intercrystalline dissolved pores, and high-quality reservoirs were concentrated in grain shoal facies. In the southern Sichuan Basin, reservoirs were dominated by intercrystalline pores, fractures, and dissolved pores, with local effective reservoir bodies found near fault zones. (3) Geochemical characteristics indicated that isotopes in the central Sichuan Basin were close to those of the contemporaneous seawater, with negative anomalies of Ce and Eu. This indicated that diagenetic fluids were mainly seawater and the reservoirs in this region were mainly controlled by penecontemporaneous dolomitization. Besides, dolomites in the southern Sichuan Basin showed negative oxygen isotope values and higher strontium isotope values than contemporaneous seawater, with a right-inclined rare earth element (REE) distribution pattern. This demonstrated that this region was affected by deep formation water and thermal fluids, and mainly experienced burial dolomitization modification. Overall, the differences in reservoirs were jointly controlled by tectonic framework, sedimentary environment, and diagenesis. The high-energy grain shoal facies in the central Sichuan Basin provided high-quality material conditions, early dolomitization preserved primary pores, and the stable tectonic environment reduced pore destruction. In the southern Sichuan Basin with a lower terrain, although dolomitization and late-stage dissolution modification in the burial environment improved porosity to some extent, the accompanying intense compaction damaged reservoir space.