The reservoir in well block Zhao 51-Tong 41 of Sulige Gas Field is a typical tight reservoir.Therefore,figuring out the genesis of tight reservoir,searching for the favorable reservoir is one of the main problems for the natural gas exploration and development in this area.Through the analysis of provenance and core observation,combining with slice identification,casting slice,cathode luminescence and scanning electron microprobe studies，we reached the following conclusions：the main lithology of sandstone in this area is lithic sandstone and lithic silicarenite with low grade of maturity.The reservoir pore structures are analyzed,and the results show the dominant types of pore are intergranular pore and intragrannular dissolved pore.Diagenesis of sandstone in this area mainly includes compaction,cementation,corrosion and metasomatism,and the compaction and cementation are the main factors of tight reservoir.Based on the analysis of diagenetic facies,we found that moderate compaction-kaolinite filling-dissolution phase and moderate compaction-calcite filling-kaolinite filling-dissolution phase are the main ones.The conclusion is that small pore space and poor connectivity of pore are the underlying cause of tight reservoir in this study area.