The changes of porosity and microcracks of high-temperature granite under water-cooling have a great influence on the safety and efficiency of geothermal resources exploitation. To analyze the formation conditions of the pore structure and microcracks of granite specimens at different temperatures under water-cooling, the rock porosity was measured by NMR, and the rock microstructure was observed by PM and SEM. The results show that the closure of microcracks occurs at 150 °C and the grain boundary microcracks appear at 300 °C. And the porosity and pore size begin to increase, the number of pores remains stable, and intracrystalline microcracks appear at 450 °C. When T = 600 °C, macropores and trans-granular microcracks appear inside the rock. When 600 °C < T ≤ 750 °C, the increase rate of porosity decreases, the number of macropores increases, the number of micropores decreases, and the total number of pores increases exponentially. The porosity and the number of macropores increase rapidly, and the aperture of transgranular microcracks increases after T = 750 °C. The change of granite microstructure leads to the decrease of thermal conductivity, which decreases with the increasing temperature. During geothermal exploitation, the thermal conductivity of dry hot rock can be characterized by porosity, and the relationship is K=C + D × E^x_.

水冷下高温花岗岩孔隙度和微裂纹的变化对地热资源开发的安全性和效率有很大影响。为分析不同温度水冷条件下花岗岩试件孔隙结构和微裂纹的形成条件，采用核磁共振测量岩石孔隙度，采用PM和扫描电镜观察岩石微观结构。结果表明，微裂纹的闭合发生在 150°C，晶界微裂纹出现在 300°C。并且孔隙率和孔径开始增加，孔隙数量保持稳定，450℃时出现晶内微裂纹。当 T = 600 °C 时，岩石内部出现大孔隙和穿晶微裂纹。当600℃<T≤750℃时，孔隙率增加率降低，大孔数增加，微孔数减少，总孔数呈指数增加。孔隙率和大孔数量迅速增加，穿晶微裂纹孔径增加T  = 750 °C。花岗岩微观结构的变化导致导热系数降低，导热系数随温度升高而降低。在地热开采过程中，干热岩的导热系数可以用孔隙度来表征，关系式为K=C + D × E ^x_。