Abstract: The key to exploration of low?porosity and low?permeability reservoirs is to predict the reservoirs with relative good physical properties to find favorable petroliferous areas. In a certain sedimentary environment, diagenetic facies is the core factor controlling the physical properties of reservoirs. The diagenetic facies which can be used to classify petroliferous areas should consider the influence of diagenesis on pore spaces of reservoirs. Based on rock components, surface porosity and petrophysical properties and through porosity evolution simulation, porosity variations before and after diagenesis such as compaction, cementation and corrosion are simulated on the basis of primary porosity. Apparent compaction rate, apparent cementation rate and apparent corrosion rate are used to represent the construction and destroy degrees of pore spaces caused by diagenesis and the degrees could be digitalized. Based on the data of apparent compaction rate, apparent cementation rate and apparent corrosion rate, diagenesis can be divided into 3 types, namely strong, moderate and weak diagenesis. Based on the intensities of compaction, cementation and corrosion, diagenetic facies can be classified quantitatively. With this method, the Permian diagenetic facies in Jinxi flexure belt of Ordos basin are classified as strong cementation and strong corrosion facies,strong cementation and moderate corrosion facies and moderate cementation and moderate corrosion facies, which is in accordance with the results from thin section analysis