Abstract: Based on the full analysis of the data such as conventional section, cast section, X-ray diffraction and SEM, the Paleaozoic clastic diagenesis and its influence on clastic reservoir development in Tazhong area have been studied. The results of the study indicate that the clastic reservoir is in the stage A of middle diagenesis and the major diagenesis includes compaction, cementation(siliceous cementation, carbonate cementation and hydrosyalite cementation), dissolution(feldspar, minor debris and carbonate cement), alternation and fracture along with the sedimentary and diagenesis history. These diagenism has markedly influenced the pore development and physical properties of the reservoir. The mechanical compaction, the subsequent volcanism of quartz and feldspar has destructive influence on the physical properties of the reservoir. Compaction and pressure solution have induced the decrease in porosity(14.1%~25.3%), the cement has filled up and blocked the pore throat of sandstone in various ways; Secondary overgrowth of quartz could fill up the primary pore and is disadvantagous to generate secondary pore. Metasomatism makes the sandstone more dense and hard while dissolution is the major diagenesis for increase of the pore space and improvement of the properties of reservoir.