During the burial process of fine-grained sedimentary rocks, with the increase of burial depth, a series of changes will occur in their mineral composition, organic matter morphology, pore type and content. In order to deeply reveal the characteristics of these changes, we tested the residual samples of organic matter thermal simulation by scanning electron microscopy, whole rock X-ray diffraction, vitrinite reflectance (R_o), rock pyrolysis and organic carbon content. It was found that the forms of organic matter changed from lump-banded to lump-like when the temperature increased from room temperature to 550 ℃. Clay minerals gradually transformed from lamellar to flocculent; the dissolution of carbonate minerals was dramatic, and the dissolution-precipitation phenomenon occured when the temperature was higher than 500 ℃. With the increase of temperature, the area of organic pores produced by thermal evolution of organic matter increased continuously. At 450-475 ℃, the organic pores reached the maximum, but when the temperature is higher than 475 ℃, the number and pore size of organic pores will decrease. As the clay minerals transformed from montmorillonite to illite-montmorillonite mixed layer and then to illite following the increase of temperature, the intergranular pores of clay minerals increase slowly at first, then increased rapidly and finally tended to be stable. The dissolution pores were mainly produced by feldspar and carbonate minerals, which were closely related to the organic acids produced by the thermal evolution of organic matter. Therefore, the change trend of dissolution pores is basically the same as that of organic matter pores, which increases slowly first and then increases rapidly, and then decreases slowly and tends to be stable. So the temperature range of 450-475 ℃, during which the number of pores and pore size are the largest, is a good reservoir.