Granite is widely recognized for their elevated radioactive heat generation and relatively high thermal conductivity, making it an important contributor to the thermal structure of geothermal systems. Existing research has primarily focused on their role as heat sources, yet their potential to facilitate heat transfer remains insufficiently explored. To address this knowledge gap, we selected South China—where heat-producing granite is extensively distributed—as our study area. We first integrated surface heat flow, heat generation values, and hot spring distribution data through a statistical analysis, with results revealing a clear spatial correlation that quantitatively confirm the positive contribution of granite-derived heat to the regional geothermal unit. Subsequently, we conducted two-dimensional numerical simulations to evaluate the thermal influence of granitic bodies under varying conditions of heat generation and thermal conductivity. The modeling results indicate that while radioactive heat contributes to crustal heating, the relatively high thermal conductivity of granites plays a critical role in enhancing vertical heat transport. This conductive effect is further strengthened in fault-related settings, underscoring the importance of structural pathways. These findings enhance our understanding of the dual thermal role of granite and provide a scientific basis for the development of targeted geothermal exploration strategies focused on thermally conductive geological units.