Abstract: To study the fracture characteristics and damage laws of high-temperature sandstone under thermal shock in water after cooling, the micro-CT technique is used to analyze the meso-pore cracks of sandstone at 600℃ under thermal shock after cooling in water at different temperatures. The relationship between the temperature of cooling medium and the pore development is analyzed, and the developing trend of fractal dimension of the pores is investigated. The results show that after the thermal shock treatment of high-temperature sandstone, a large number of new pores sprout, and the throat is generated in the fragile place between the pores and gradually develops and expands. Eventually, a large number of pores are connected to form pore clusters. With the decrease of the temperature of the cooling medium, the volume of the connected clusters increases, the permeability increases, and the damage degree increases. The volume fraction of the pores of sandstone is linearly and positively correlated with the fractal dimension. The larger the volume fraction of the pores, the larger the fractal dimension, and the more severe the damage of sandstone. The fractal dimension can be used to characterize the damage degree of sandstone. The pores and fracture characteristics of granite, limestone and sandstone at 600℃ are quite different under thermal shock after cooling in water. The granite is characterized by obvious brittle fracture, for the sandstone, the pore development is obvious, and for the limestone, there are pores and fractures.