Abstract: Based on comprehensive analysis of cast thin?section, SEM, X?ray diffraction, petrophysical property data, this paper presents the diagenesis types of compaction, cementation and dissolution existed in the Badaowan reservoir of Lower Jurassic, and points out that its diagenesis stage is now in period A of mid?diagenesis, and the reservoir quality is obviously influenced by the diagenesis. The coal measure strata of Badaowan formation belong to diagenetic environment of acidic fluid. The early dissolution of clastic particles and the high content of the reservoir plastic particles result in stronger diagenesis in it, by which its porosity drops dramatically by averaging28.75%, followed by continuously reducing due to existence of kaolinite, calcite and siliceous cements by3.03%in average. The late dissolution of feldspar grains forms intragranular dissolved pores which improve the reservoir porosity by averaging1.15%. Comprehensive analysis shows that midcoarse sandstone has high content of rigid grains, low content of plastic lithic fragments, and stronger compaction resistance, which is the most favorable reservoir sandbody