Abstract: Cooling shock is an effective method to increase the permeability of geothermal reservoir by causing fractures on high temperature rock. For the purpose of quantitatively analyze the damage degree of granite caused by cooling shock at different heating temperatures and explore the damage mechanism under the action of cooling shock, the damage of high temperature granite samples under was analyzed under natural cooling and water cooling conditions by means of thin section observation and SEM scanning technology. The results show that when the heating temperature is increased from 200°C to 800°C, the crack density of the section A at the center of the rock sample increases by 17.6%-144.7% and 27.6%-163.7% respectively under natural cooling and water cooling. For the slice B 12.5 mm away from the center of the circle, the fracture density increases by 40.1%-202.8% and 61.3%-222.7% under natural cooling and water cooling conditions, respectively. The results also show that the damage degree of granite increases with the increase of heating temperature, and the damage degree of granite is greater when it is cooled by water than in air. In addition, the damage degree of granite is greater when it is closer to the sample surface due to the existence of thermal gradient. These conclusions not only provide experimental reference for understanding the effect of cooling shock on the damage of high-temperature granite, but also play a very important role in guiding the application of thermal stimulation method in reservoir reconstruction.