The dissolution and transformation of feldspar particles in acidic fluid environments are the important cause of the formation and evolution of secondary pores in sandstones. Such diagenesis has an important influence on the formation，evolution，and distribution of favorable reservoirs in deep oil-bearing basins. Authigenic kaolinite is the main diagenetic product in the transformation process of feldspar particles in acidic fluid environments. Its genetic mechanism and occurrence affect the types of reservoir pores formed during this process. Taking Shahejie Formation in Dongying Sag as an example，this paper used numerical simulation method based on the thermodynamics to clarify the formation process of authigenic kaolinite under different formation temperatures. In addition，it employed means such as cast thin sections and scanning electron microscopy to reveal the genetic mechanisms and feldspar transformation process in different diagenetic environments. The results show that when the formation temperature is higher than 120 ℃ ，the autogenic kaolinite in the reservoirs is the transformation product of gibbsite and feldspar. The secondary pores formed during this process are intercrystalline micropores of kaolinite，and the pore structure is the micropore-fine throat. When the formation temperature is lower than 120 ℃，the authigenic kaolinite in the reservoirs is the product of pore fluid precipitation or the combination of gibbsite and silica-containing particles. The secondary pores formed during this process are macropores resulting from feldspar particle dissolution，and the pore structure is the macropore-coarse throat.