With the rapid development of in-situ shale conversion mining technology, it is particularly important to study the change of physical and mechanical properties of shale and the law of fracture propagation under the action of high temperature water heating. First, the samples were subjected to high temperature treatment at different temperatures and pressures. Then, the samples were subjected to acoustic wave test, permeability test, Brazilian splitting test and uniaxial compression test. It is found that in the range of 25–450 °C, with the increase of hot fluid temperature: (1) The number of pores and micro-fractures in shale increases. (2) The measured permeability of shale gas gradually increases. (3) The tensile strength and compressive strength of shale gradually decrease. In addition, the high temperature and high pressure reactor independently designed by the laboratory is used to treat the shale. The above research has practical significance for elucidating the shale fracture propagation mechanism under the action of high temperature water, and will also provide help for the development of in-situ shale conversion mining technology.