Using data such as ordinary thin sections，casting thin sections，scanning electronm icroscope observaˉtions and testing，we quantitatively calculate the diagenesis intensity parameters such as compaction，cementation and dissolution，which influence physical properties of the Lower Cretaceous reservoirs in the Tanzhuang sag，southern North China Basin.The apparent rates of compaction，cementation and dissolution porosity in different wells and intervals are obtained and the division standards of diagenesis intensity are determ ined.The Lower Cretaceous reservoirs are divided into five types of diagenetic facies.The typeˉⅠand typeˉⅡare good reservoir facies belts，the typeⅢis fair reservoir facies belt，while the typeⅣand typeˉⅤare poor reservoir facies belts.By predicting distribution ofdiagenetic facies and in combinationwith study ofdepositional systems and distribuˉtion pattern of secondary pores，we believe that the northern part of the southern fan delta and the southern part of the northern delta in the Tanzhuang sag，with moderate toˉrelatively high compaction，high cementation and moderate dissolution，are favorable reservoir facies belts for each interval.