Abstract: Based on thin section,geochemical analysis,cathode luminescence and fluid inclusion,a detailed study of the diagenesis types and sequence of the lower-middle Ordovician Yingshan formation carbonate rocks and their relationships with porosity evolution in Yubei area was carried out.The results show the reservoir of the lower-middle Ordovician Yingshan formation in Yubei area is subjected to such diageneses as penecontemporaneous dolomitization,burial dolomitization,3 phase dissolution,3 phase cementation,filling,compaction and pressolution,among which the dolomitization and dissolution act as the significant effects on the reservoir.According to the order and porosity evolution characteristics in diagenesis,the diagenetic sequence and porosity evolution of Yingshan formation were summarized.