Microscopic pore structure is of great significance to the exploration and utilization of shale oil and gas reservoirs. Taking the deep shale samples of Songke No.2 well as the research object， the mechanical properties and pore changes of shale under the action of heat and liquid were studied. The microscopic pore characteristics of saturated and heated shale were compared by means of field emission scanning electron microscopy （SEM）， high pressure mercury injection and CT scanning. The results show that the main pore types of the shale samples include micro-cracks， intergranular pores， intragranular pores， etc.， among which more micro-nano cracks are produced， and the main size range is 20nm-400nm. The saturated humidity and high temperature heating will reduce the pore volume， porosity and permeability of shale， and the higher the temperature， the more obvious the effect. The nano-scale pore shrinkage of saturated samples decreases， the proportion of 1μm-35μm increases， the proportion of pores larger than 35μm decreases， and the internal macro-fractures are filled with water-absorbing expansive minerals. The nano-scale pores of the heated sample crack to both sides， and the 40nm-100nm pores are converted into hundreds of nanometers or even micron-scale pores. The proportion of 1μm-50μm pores increases， and the internal wide cracks are filled to form small round-hole cracks. At the same time， the three-dimensional pore model of the shale samples obtained by CT scanning is reconstructed by computer software to provide a clearer and more realistic three-dimensional display and quantitative study on the surface and internal micro-pores of shale was carried out.