The Anyue gas field contains deeply buried multilayer carbonate reservoirs and is a prominent natural gas producer in China. Although prior research mostly focused on the Sinian and lower Cambrian reservoirs, the middle–upper Cambrian Xixiangchi reservoir remains less explored. A comprehensive grasp of the diagenetic fluid history of the Xixiangchi Formation has yet to be achieved. This study uses a multifaceted approach, incorporating various petrographic observations (transmitted light, ultraviolet light, reflected light, and cold cathodoluminescence), fluid inclusion microthermometry, Raman spectrometry, one-dimensional basin modeling, and fluid pressure–temperature modeling to unravel the basin evolution with respect to the Xixiangchi Formation in the Anyue region with a specific focus on the fluids. The investigation reveals a diagenetic sequence encompassing multiple dolomite phases (1–6), bitumen occurrences, quartz, and calcite. Two distinct types of pyrobitumen (1 and 2), originating from degraded oils in surface–near-surface environments and reservoir oil in situ thermal cracking at depth, respectively, were identified. Fluid pressure–volume–temperature–composition modeling indicates that the pseudosecondary gas and aqueous inclusions in quartz were coevally trapped near pressure–temperature conditions of ∼235°C and ∼130 MPa (∼55 MPa over the hydrostatic gradient), corresponding to maximum burial (∼7500 m) at ca. 91 Ma (Late Cretaceous, late Yanshanian movement), whereas the primary inclusions in dolomite 6 were trapped at ∼180°C and ∼100 MPa (∼45 MPa over the hydrostatic pressure), corresponding to ca. 150 Ma (Late Jurassic, early Yanshanian movement). Furthermore, the absence of methane or methane-bearing aqueous inclusions in calcite is hypothesized to be a result of gas leakage before calcite precipitation. This study provides insight into the temperature stability of hydrocarbon compounds in high-temperature reservoirs, enhancing our insight into deeply buried reservoirs, effectively serving as a tool for superior reservoir development within prime zones, while reducing exploration hazards and operational expenditures.