Supergene karst is regarded as one of the crucial genetic mechanisms responsible for the karst geothermal reservoir of the Majiagou Formation in the western Luxi Uplift. However, the controlling factors and how to modify the karst geothermal reservoir of supergene karst have not yet been thoroughly investigated by previous researchers. In order to investigate the main controlling factors and modification of geothermal karst reservoirs of supergene karst in the study area, an integrated methodology combining field outcrop and core observations, well logging and geochemical data analysis, as well as tectonic-sedimentary evolution interpretation was used. This approach was applied to characterize the supergene karst features in the Majiagou Formation in the western Luxi Uplift, analyzed its controlling factors, and assessed its impact on reservoir quality. The results show that the depth of supergene karst in the study area is constrained to within 200 m below the unconformity at the top of the Majiagou Formation, where limestone-type weathering crust karst is predominantly developed. The most prominent identification markers about supergene karst are characterized by high-angle dissolution fractures, weathering residual layers, drilling fluid loss, and significant negative shifts in δ13 CPDB and δ18 OPDB values. Supergene karst is jointly controlled by internal factors ( lithology and mineral composition, as well as rock layer structure and assemblage) and external factors ( paleoclimate, exposure duration, and tectonism ) . The tectonic uplifts during the Caledonian and Himalayan periods are considered to be the critical factors for the development of supergene karst. During the Caledonian period, the humid and rainy climate, combined with tectonic uplift, resulted in the exposure and dissolution of the carbonate rocks of the Majiagou Formation in the study area, leading to intensive supergene karst. The modification of limestone-type weathering crust reservoirs by supergene karst is characterized by vertical alteration features. After analysing features and main controlling factors of supergene karst, it is concluded that supergene karst are recognized for their dualistic influence on reservoir physical properties. On one hand, the development of extensive dissolution pore-cavity-fracture networks can be observed to substantially enhance reservoir quality; on the other hand, the cementation effects occurring within the karst slow-flow zone, together with the karst collapse and weathered residual layers caused by excessive exposure, are found to significantly degrade reservoir physical properties.